It’s often a copout for some Christians to avoid doctrine by using some language which implies that living for God is all about your heart. Jesus answered the scribe in Mark 12:30, “And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment.” So according to Christ it’s not just our hearts, but our mind and strength as well.
In fact if you read Paul’s prayers, he repeatedly prays for the believer’s knowledge and understanding which is very telling. At the same time, Jesus prayed in Matthew 11:25, “thou hast hid these things from the wise and prudent, and hast revealed them unto babes.” So while the heart is the true reflection of a man, a man’s heart is shaped by his understanding. But that understanding can only develop in a spirit of childlike humility.