The following is a quotation from: http://www.ptgbook.org/index.html and I do agree mostly with what he says about this particular issue except that it is NOT even to even. To learn Why it is NOT even to even, please read the When Does the Day start article. Also, the first day of the month when to start counting the days of the month should be according to the New Moon events.

The Days of Unleavened Bread - Repentance Immediately after Passover day are the seven days of unleavened bread. The first day and the last day of the seven (the seventh day) are holy days, Sabbaths, days of rest and assembly. The instructions for these days are given in Exodus 12:14-20, and Exodus 13:3-10, as well as various other places. During these days, only unleavened bread is to be eaten, and nothing with leavening is to be eaten or even kept in the home. For ancient Israel, this represented leaving Egypt in haste because they had no time to prepare leavened bread. But like Passover, these days are still in effect today for God's Church, and like Passover, they have deep meaning beyond the limited understanding given to ancient Israel. What does leavened or unleavened bread represent in the New Testament? In the context of the time of Passover and the days of unleavened bread, Paul used leavening to represents sin, and unleavened bread to represent righteousness. Notice what Paul said in 1 Corinthians 5:6-8: "Your glorying is not good. Do you not know that a little leaven leavens the whole lump? Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us. Therefore let us keep the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth." Here Paul likens leavening to malice and wickedness, but likens unleavened bread to sincerity and truth. He also says, "let us keep the feast." What feast is he talking about? The context indicates he is talking about the Feast of Unleavened Bread that God gave Israel at the time of the Exodus. This shows that the days of unleavened bread were being kept by Paul and the New Testament Church of God. And since Paul was primarily an apostle to the gentiles (Romans 15:15-16, Galatians 2:7-9), this indicates that Paul understood that these days were not just for the Jews but were for gentile Christians as well. What lessons can we learn from the days of unleavened bread? Jesus Christ was sacrificed for us so we can be forgiven, and this is pictured by Passover. But we also have our part to perform. We must repent and strive to put sin out of our lives. Christ paid the penalty for our sins so our sins can be forgiven, but that does not give us permission to continue sinning. We have to repent. After the disciples received the Holy Spirit, when Peter spoke to the crowd, he told them to repent. "Now when they heard this, they were cut to the heart, and said to Peter and the rest of the apostles, 'Men and brethren, what shall we do?' Then Peter said to them, 'Repent, and let every one of you be baptized in the name of Jesus Christ for the remission of sins; and you shall receive the gift of the Holy Spirit. For the promise is to you and to your children, and to all who are afar off, as many as the Lord our God will call' " (Acts 2:37-39). Paul wrote, "do not sin" (1 Corinthians 15:34). Keeping the days of unleavened bread represents and helps to teach us our part in God's plan, that we have to repent and strive to put sin out of our lives. We avoid leavening for seven days to learn that we need to avoid sin in our lives, and we eat unleavened bread for seven days to help learn the lesson that we need to put the righteousness of Jesus Christ into our lives. We need to study His teachings, obey His commands, and follow His examples. The Bible commands that men repent. What do we need to repent of? We need to repent of sin, but we also need to repent of our own sinful nature and be willing to let God clean up our character and give us a new nature based on God's righteousness, not our own. We need to repent of the entire direction of our lives and be willing to begin to go in a new direction. We have to be willing to give our lives to God in one hundred percent obedience and service for the rest of our lives. We have to be willing to love God with all our heart and our neighbor as ourselves. This love is more than just an emotion, though it may have an emotional quality, but it is a strong commitment of the will. Love towards God must include the submitting of the human will to God's will, as Jesus did, setting an example for us. We have to be willing to strive to live by every word of God. The writer of Hebrews says that repentance from dead works is one of the elementary principles we need to understand (Hebrews 6:1). We need to repent of sin, but to do this, we need to know what sin is. Many people think that sin is doing what they think is wrong. They think that sin is whatever violates their conscience. This is not true. Sin is not the violation of our conscience, it is the violation of God's law. 1 John 3:4 states, "Whoever commits sin also commits lawlessness, and sin is lawlessness." In the King James Version this reads, "Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law." It is the law of God that defines sin, not our conscience. Paul gives an example. In Romans 7:7 he says, "What shall we say then? Is the law sin? Certainly not! On the contrary, I would not have known sin except through the law. For I would not have known covetousness unless the law had said, 'You shall not covet.' " It is the commandment against coveting that taught Paul that it was a sin to covet, because God's law and commandments DEFINE right and wrong. That is why sin is the transgression of the law of God. Many people think that whatever a person does, it is not a sin if they don't think it is wrong. That is not true. A person can be sinning against God and not even know it. Notice what Jesus said about those who sinned but did not think they were doing anything wrong. "And that servant who knew his master’s will, and did not prepare himself or do according to his will, shall be beaten with many stripes. But he who did not know, yet committed things deserving of stripes, shall be beaten with few. For everyone to whom much is given, from him much will be required; and to whom much has been committed, of him they will ask the more" (Luke 12:47-48). Notice that Jesus did not say that those who did not know their master's will were free from guilt and would not be beaten at all. He said their guilt was less in comparison with the person who knew God's will and knew what they were doing was wrong, and therefore their punishment would be lighter, nevertheless, this shows that there is guilt, and punishment, for the person who violates God's law even if that person does not know it, and therefore the violation of God's law is sin. Mankind has taken the path of each person deciding for himself or herself what is right or wrong instead of recognizing that it is God only who had the prerogative to decide right from wrong, sin from righteousness. Repentance involves acknowledging that God defines sin, and we have to look to God and His Word the Bible, and to God's law and commandments to know what is right and wrong, and then strive to live the right way according to God's will and instructions. Repentance includes a lifelong commitment to turn from the direction of pleasing the self to the direction of loving God with all our being and loving our neighbor as ourselves (Matthew 22:37-40). It is a new way of life based on God's law of love. It requires striving to live, not only according to the letter of God's law, but the spiritual intent of God's law as well. Notice the examples Jesus gave about the requirement to obey the spirit of the law as well as the letter. "Ye have heard that it was said by them of old time, Thou shalt not kill; and whosoever shall kill shall be in danger of the judgment: But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire" (Matthew 5:21-22, KJV). "Ye have heard that it was said by them of old time, Thou shalt not commit adultery: But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart" (Matthew 5:27-28, KJV). Also, since we are required by God's law to love God with all our being and might, this includes living our lives to please Him in everything we do and striving to submit our wills to His will in everything. This goes beyond just obeying God's explicit commandments. This includes striving to know God's will (by studying and believing God's word, the Bible), and then striving to DO God's will. Jesus set the example by doing not only what the Father commanded Him, but the Father's will also. "Jesus said to them, 'My food is to do the will of Him who sent Me, and to finish His work' " (John 4:34). Just before Jesus was crucified, He prayed to the Father that if it was the Father's will, Jesus would be spared this suffering. Nevertheless, Jesus requested that this be done ONLY if it was the Father's will. "And he was withdrawn from them about a stone’s cast, and kneeled down, and prayed, Saying, Father, if thou be willing, remove this cup from me: nevertheless not my will, but thine, be done" (Luke 22:41-42, KJV). Notice also John 5:30, " I can of mine own self do nothing: as I hear, I judge: and my judgment is just; because I seek not mine own will, but the will of the Father which hath sent me" (KJV). And John 6:38, "For I came down from heaven, not to do mine own will, but the will of him that sent me" (KJV). And John 8:29, "And he that sent me is with me: the Father hath not left me alone; for I do always those things that please him" (KJV). Repentance involves making a lifetime commitment to strive to always do the things that please God, because this is part of obeying the greatest commandment, you shall love God with all your heart. Repentance requires a commitment to strive to live by every word of God. When Jesus was tempted by Satan, he resisted and countered every temptation by referring to Old Testament scripture. For example, note Matthew 4:3-4, "Now when the tempter came to Him, he said, 'If You are the Son of God, command that these stones become bread.' But He answered and said, 'It is written, "Man shall not live by bread alone, but by every word that proceeds from the mouth of God." ' " Repentance also requires that we acknowledge our guilt before God, that we are sinners, and ask God to clean us up. We have to come to realize that our very nature is sinful. "The heart is deceitful above all things, And desperately wicked; Who can know it?" (Jeremiah 17:9). Everyone has sinned and is in need of forgiveness, "for all have sinned and fall short of the glory of God" (Romans 3:23, see also Romans 5:12). When David repented after his sin in the matter of Uriah the Hittite, he acknowledged his guilt before God. "Have mercy upon me, O God, According to Your lovingkindness; According to the multitude of Your tender mercies, Blot out my transgressions. Wash me thoroughly from my iniquity, And cleanse me from my sin. For I acknowledge my transgressions, And my sin is always before me. Against You, You only, have I sinned, And done this evil in Your sight- That You may be found just when You speak, And blameless when You judge" (Psalm 51:1-4). "Hide Your face from my sins, And blot out all my iniquities. Create in me a clean heart, O God, And renew a steadfast spirit within me" (Psalm 51:9-10). The days of unleavened bread are given to us by God to help teach us the lesson that we have to repent and strive to put sin out of our lives, represented by leavening, and to put God's righteousness into our lives, represented by the unleavened bread that we eat. This is one of the major steps in God's plan for the salvation of mankind, and it is illustrated by this feast of God. The Church of God observes the days of unleavened bread by getting all leaven and leavened products out of our homes and avoiding eating anything with leaving in it (yeast, baking soda, baking powder, etc.) for seven days, and also eating unleavened bread during this time (matzos for example, although some members make their own unleavened bread). We observe the first and last of the seven days by refraining from work and by assembling for church services, as on the weekly Sabbath, as commanded by God (Exodus 12:16). Also, on the evening of the First Day of Unleavened Bread (the next night after the Passover observance), we keep the Night to Be Much Observed, which is a separate event from Passover, by getting together in families and small groups in each others' homes or meeting places and sharing a meal. For ancient Israel, this observance represented coming out of Egypt, which occurred on the night following Passover night (Exodus 12:40-42). For the Church, it represents coming out of the bondage of Satan's deception and the sinful ways of this world.