In chapter 10 of the Gospel of Mark, we see Jesus interacting with various groups of people and reminding them (and us) that our hearts are often hardened toward the things of God. It is necessary to receive Him like a child, to put away any idols in our heart which crowd out God, and to serve others.
In Mark 10:45 Jesus explains the reason for His entry into our world:
For even the Son of Man came not to be served but to serve, and to give his life as a ransom for many.
Mark 10:45 (ESV)
The Son of Man is a title of honor and eternal power in the Bible. Yet the Son of Man voluntarily came to Earth to take the penalty for our disobedience to God.