If Jesus was God, why would he send his life in heaven to the womb of Mary?

There is a Holy Trinity that bears Godhood. I John 5:7 says, "There are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one." Jesus Himself said in John 10:31, "I and my Father are one." The father was in Heaven saying, "This is My beloved Son" while Jesus was coming up out of the water from His baptism -- at the same time, the Holy Spirit was descending upon Him in the form of a dove.

That answers "how." The "why" is found in the verse that every Sunday School child above the age of four has memorized: John 3:16. "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life." Why did the Father send the Son down to earth? Because He loves us and wants us to spend eternity with Him. However, we are sinful creatures and cannot be with a holy God ("Then said Jesus again unto them, I go my way, and ye shall seek me, and shall die in your sins: whither I go, ye cannot come" -- John 8:22.) But the sinless Son of God paid the penalty for every person. ("For he hath made him to be sin for us, who knew no sin; that we might be made the righteousness of God in him" -- II Corinthians 5:21). He shed His innocent blood, just as the Old Testament spotless lambs gave their blood, to cover the sins of the people ("And almost all things are by the law purged with blood; and without shedding of blood is no remission" Hebrews 9:22). So now we can be saved from the penalty of sin, since this "salvation" is paid. The reason some are yet in their sins is because they have not asked for their sins to be forgiven through the blood of Jesus. Remember Jesus' words, "I am the way, the truth, and the life: no man cometh unto the Father but by me" (John 14:6).

I asked for that forgiveness as soon as I began to truly understand how much I needed it at the age of 13. Anyone, absolutely anyone, regardless of gender, ethnic, monetary, famous, moral, or powerful status or lack thereof can be saved, too, by simply asking for that forgiveness. I hope to see you in Heaven as well as seeing God.

Hope that helps. :-)

[All verses quoted from the King James Version]