The church has been growing. The Lord was adding to their number day by day those who were being saved (Acts 2:47). Peter has a captive audience because a beggar lame from birth was publicly healed.
The people are marveling at this miracle. Peter asks them, "Why are you amazed at this?" He points out their unbelief. Then he points them to Christ. Two passages from Moses serve as foundation texts.
After this message more believe: But many of those who had heard the message believed; and the number of the men came to be about five thousand (Acts 4:4, NASB).
Deuteronomy 18:15 in Context
Moses is giving instruction for after entering the Promised Land. He commands them to be holy. He teaches that whoever participates in the profane practices of the pagans will be detestable to God.
Then, Moses promises that God will raise up a prophet for them to obey.
"The LORD your God will raise up for you a prophet like me from among you, from your countrymen, you shall listen to him. This is according to all that you asked of the LORD your God in Horeb on the day of the assembly, saying, 'Let me not hear again the voice of the LORD my God, let me not see this great fire anymore, or I will die.' The LORD said to me, 'They have spoken well. I will raise up a prophet from among their countrymen like you, and I will put My words in his mouth, and he shall speak to them all that I command him. It shall come about that whoever will not listen to My words which he shall speak in My name, I Myself will require it of him.'" (Deuteronomy 18:15-19, NASB)
This passage does not speak of the Lord raising up prophets (plural). It speaks of raising up a prophet.
This was taken to be a messianic promise. The Jews living in Jerusalem would have understood immediately that Peter was appealing to a text that prophesied the coming Messiah.
Genesis 22:18 in Context
This is one of the most famous passages in Scripture. God tested Abraham by telling him to sacrifice Isaac.
Isaac was the child of promise. His birth had been promised by God to Abraham and Sarah. In Genesis 15 Abraham was promised a son. In Genesis 16 we see Abraham having a child through his wife's maid, Hagar. This child, Ishmael, is not the child of promise. Ishmael is born to Abraham when he is 86 years old (Gen 16:16).
In Genesis 18 we again read of the promised child to come through Abraham's barren wife, Sarah. This promise is made thirteen years after the birth of Ishmael. Abraham was 99 years old.
Isaac is born the following year. Abraham is 100 (Gen 21:5).
God is foreshadowing the sacrifice of His own Promised Son, the Messiah. God does not make Abraham follow through on what He Himself will do by offering His own Beloved Son Jesus to die on the cross.
After Abraham's willingness to sacrifice Isaac is demonstrated God once again reiterates His plan to bless the nations through Isaac.
Then the angel of the LORD called to Abraham a second time from heaven, and said, "By Myself I have sworn, declares the LORD, because you have done this thing and have not withheld your son, your only son, indeed I will greatly bless you, and I will greatly multiply your seed as the stars of the heavens and as the sand which is on the seashore; and your seed shall possess the gate of their enemies. In your seed all the nations of the earth shall be blessed, because you have obeyed My voice." (Genesis 22:15-18, NASB)
How Peter uses Moses
Both passages appear in books written by Moses. Deuteronomy 18 records a prophesy in Moses' own lifetime. Genesis 22 predates Moses by roughly 600 years. Peter is appealing to a line of promises that were made by God 2,000 and 1,400 years before his present day.
Peter is confronting the unbelief of the people by citing these promises. Peter uses these texts to show that God is doing what He has said He would do.
In their unbelief they are amazed at this demonstration of God's power.
In their unbelief they handed over the Promised Messiah to be crucified.
In contrast, the healing took place because of the man's faith in the name of Jesus.
Peter calls his hearers to repent of their unbelief. To return to God by faith. As Jews, they trust that by lineage they are the sons of the prophets and the covenant. Peter claims that if this is true, then they should take hold of the fulfillment of the promised Messiah by putting their faith in Christ. He is the One of whom they spoke.
Peter proclaims that all of the prophets have announced the coming of the Prophet since the beginning until their present day. These prophecies were all built on the foundation found in Moses' writings.
Peter concludes by showing that this promise contained a call to holiness. The promised blessing comes for those who obey the Promised Messiah. Therefore, the proper response is not simply faith. It is repentance and faith.
Many seek the blessing of God. Many people think of blessing contrary to how Peter defines it.
"For you first, God raised up His Servant and sent Him to bless you by turning every one of you from your wicked ways."
(Acts 3:26, NASB)
Blessing comes through faith and obedience. God's children understand that it is a blessing to obey our heavenly Father. He is not an oppressive dictator. He is not holding out on us.
Consistently Scripture declares that following our own lusts and impulses is slavery. It's a curse.
Christ came to call a people to God. He came to bless us. Jew first, then Gentile. By turning us from our wicked ways to His holy ways. He came to shed His own blood for the forgiveness of our trespasses so that we could receive life and peace by putting our faith in Him.
Many today believe that we can come to Christ without forsaking our former way of life. Many preach a gospel of salvation without repentance.
This is contrary to the promised blessing. This is contrary to the ministry of the Promised Prophet.
We are blessed by turning from our disobedience, believing in Him for salvation, and obediently following Him until the end.