Verse 4 is loaded with a bunch of good stuff. First, “But when the fullness of time had come…” At the right time, according to God’s plan and purpose, His plan to save all people (not just His chosen people) went into effect. Next, “God sent forth his Son” – true God – “Born of woman” and yet true man. Somehow, Jesus was fully God and fully man at the same time, both are very necessary for the task He was given.
The next part is the key, “born under the law to redeem those who are under the law.” That’s the reason He needed to be fully man, to save all of us. We were born under the law, born under the effects of the law, born under sin and death. We can’t keep the law perfectly – not only for a day. The only way we could be saved from that was for one to fulfill the law perfectly in our place. Jesus did that by His life on this earth as the only person who did not sin.
Because of our faith in Jesus, we are no longer slaves (to the law and sin), but we are His adopted children. Do you know what’s so neat about being adopted? God loved us so much that He chose to make us His children, given full rights, including the right of eternal life!