But be sure to fear the Lord and serve Him faithfully with all your heart; consider what great things He has done for you. 1 Samuel 12:24
I suppose many would see these as contradictions: following one's own heart and serving God with one's whole heart might seem mutually exclusive.
But I have long believed that they are the same thing when we put God first in our lives. God has gifted each person in very specific ways. When we follow God, we will follow the heart He has put within us.