Hebrews 3:12

Take care, brothers and sisters, that there not be in any one of you a wicked, unbelieving heart (which refuses to trust and rely on the Lord, a heart) that turns away from the living God. 

We have to be careful not to give God lip service but to truly believe in Him in our hearts. Sometimes, we have to pause and examine our hearts and our relationship with God. It is necessary for every believer to guard what we hear, see, and spend time around. When we keep our faith stirred up and reassured with the word, our hearts will remain close to God.