Christians glibly state that Jesus came to save people from their sins, and that is true. But what does it mean? In verse 4, we are told that He was born under the law, and verse 5 says He came "to redeem them that were under the law."
--To what law is Paul referring? In the context of the Galatian letter, it seems to be Torah, the law which was given by God through Moses. Jesus was born under this law, that is what is referred to in verse 4. He was born a Jew. But there is another law more basic than Torah, which applies to everyone.
Jesus, when asked what the most important commandment was, summed up all of the Old Testament this way:
"Mat 22:37 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. 38 This is the first and great commandment. 39 And the second is like unto it, Thou shalt love thy neighbour as thyself. 40 On these two commandments hang all the law and the prophets."So if one does not love God and one's neighbor in this way all the time one has sinned, and is under the law spoken of in Galatians 4:5. Since no one can do this all the time, everyone has sinned, and "... the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord. (Rom 6:23) This is the other law--the law of sin and death.
The point is, we cannot do enough to make up for even one sin. But Jesus came to release us from doing work to try to be good enough for God. Keeping the law is a burden we cannot bear; it is too heavy. But Jesus kept the law, and paid the penalty we owe for not keeping it, for us. As soon as we realize that we can't, but Jesus did, we can relax and accept God's gift of life through Him. That was the purpose of His coming; to give us life.