God is a God of purpose and does nothing without a reason. Jesus was sent to earth by God for a purpose, which He started and finished. An understanding of this purpose will help you to appreciate the coming of Christ and His mission on earth.
And she will bring forth a Son, and you shall call His name Jesus, for He will save His people from their sins." Matthew 1:21 (NKJV)
Now all things are of God, who has reconciled us to Himself through Jesus Christ, and has given us the ministry of reconciliation, that is, that God was in Christ reconciling the world to Himself, not imputing their trespasses to them, and has committed to us the word of reconciliation -2 Corinthians 5:18-19 (NKJV)
And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled in the body of His flesh through death, to present you holy, and blameless, and above reproach in His sight--- Colossians 1:21-22 (NKJV)
The thief does not come except to steal, and to kill, and to destroy. I have come that they may have life, and that they may have it more abundantly - John 10:10 (NKJV)
Jesus Christ came to save, reconcile men back to God and give them life in abundance.
Salvation of souls
When the angel of the Lord visited Joseph to assure him that it was okay to take Mary as his wife, he gave him the name of the baby and his purpose on earth: to save His people from their sin.
God, from the time of the fall of man via Adam, made a plan to redeem man from his fall and restore him to his original position before the fall. When the Lord created man he was without sin before Him and only knew sin when they disobeyed God and ate the forbidden fruit (Genesis 3:1-11). So, through Adam, sin entered the world and people became sinners (Romans 5:12, 19).
Jesus was God's wisdom and power (1 Corinthians 1:24) to save man from his sins and restore him to his original state before the fall. In Genesis 3:15, God declared this plan of victory over the devil - the Seed of the woman was to defeat the devil. The enemy expected it, tried to abort it many times but failed because he didn't know how God was going to execute His plan.
When the birth of Jesus was announced to King Herod by the wise men from the east, the enemy tried to kill Jesus through Herod but he failed, he only succeeded in killing innocent babies - Matthew 2:1-18. And when Jesus started His ministry fully, the devil tried many times too to kill Him through the people (Luke 4:28-30) but couldn't touch Him because it wasn't time for His death (Luke 22:53).
The wisdom of God was a great mystery to them because if they had known it, the devil would not have allowed the people to crucify Jesus (1 Corinthians 2:7-8). He thought Christ's death would be his victory not knowing it was going to be his downfall (Colossians 2:13-15).
Christ, who knew no sin, became sin that we might be saved and become the righteousness of God (2 Corinthians 5:21). On the cross, Christ carried our sins in our place so that we can be pure before God, our sins were washed away and we stand totally new before God; old things are passed away and behold all things have become new (2 Corinthians 5:17).
God is of purer eyes than to behold iniquity (Habakkuk 1:13). So, when Jesus was on the cross with the sins of humanity, God turned His back on Him and that was why Jesus cried out, "My God, My God, why have you forsaken Me?" - Matthew 27:46 (NKJV). For the first time, Christ addressed God as God instead of Father as He had always done. But He achieved His purpose which was to save man. Now anyone who receives Him receives the gift that was fully paid for: sins washed away and salvation of soul.
Reconciliation unto God
Before the fall of man, man was having a great fellowship with God. It was recorded that the Lord came in the cool of the day calling on Adam, and then confirmed that Adam had disobeyed Him (Genesis 3:8). This shows that they had an intimacy before the fall. When man sinned against God in the Garden of Eden, the Lord drove them out of the garden and the usual fellowship between God and man ceased.
So, part of God's plan for salvation of man was to reconcile man back to Himself through Christ and not remember the sin that put up the barrier between them. Christ made peace through the blood of His cross (Colossians 1:20).
Now, every believing Christian receives the spirit of adoption at new birth by whom he cries out, "Abba, Father" (Romans 8:15). You can now relate with God as a father and son would. Before your salvation, God was just your maker but now He is also a father to you, since you received His son as your savior.
Christ, through His death had reconciled you to God, to present you holy, blameless and above reproach in His sight. You can now come boldly unto the throne of grace to obtain mercy and find grace in time of need (Hebrews 4:16)
The enemy's mission on earth is to steal, kill and destroy but Christ came to give us life and to give it to us more abundantly (John 10:10). Everyone who has left houses or brothers or sisters or father or mother or wife or children or lands, for Christ's sake, shall surely receive many times more in this present time and in the age to come eternal life (Matthew 19:29). This is abundant life.
Galatians 3:13-14 makes it clear that Christ had to go to the cross to deliver the blessings of Abraham to us as promised by God in Genesis 12:1-3: in you shall all families be blessed. Abraham was a great nation and a blessing, those who blessed him were blessed by God and those who cursed him were cursed by God. Abraham enjoyed abundant life and Christ was hanged on the cross that we may be partakers of these blessings.
Abundant life is life without sickness or disease, filled with wealth and riches, coupled with a tremendous spiritual growth (3 John 2). It is also a life full of power, and riches, and wisdom, and strength, and honour, and glory, and blessing - (Revelation 5:12)
Furthermore, abundant life is long life till you are satisfied (Psalm 91:16), like Paul who had to choose whether to continue living or not. However, he chose to live for the sake of the spiritual growth of the Philippians (Philippians 1:21-26).
In conclusion, Jesus Christ's mission on earth was to obey God (Hebrews 10:5-7) and restore man to his original spiritual position that would give him unlimited access to God and to all that He can offer (Romans 8:17)