It is a change of government in your heart from self-rule to the Lord Jesus Christ. Since Christ is God and died and rose from the dead to save you, He is more important than your job, family, career and even your life itself.
In Luke 14:26, Jesus says that if a person would be His disciple, he must put Him first before all the things of the world, even his own life.
When you surrender and completely trust Him in this way, God will put His Spirit in you and you will be born into God’s family.