To keep the heart then, is carefully to preserve it from sin, which disorders it; and maintain that spiritual frame which fits it for a life of communion with God.
1. Frequent observation of the frame of the heart. Carnal and formal persons take no heed to this; they cannot be brought to confer with their own hearts: there are some people who have lived forty or fifty years in the world, and have had scarcely one hour’s discourse with their own hearts. It is a hard thing to bring a man and himself together on such business; but saints know those soliloquies to be very beneficial. The heathen could say, “the soul is made wise by sitting still in quietness.” Though bankrupts care not to look into their accounts, yet upright hearts will know whether they go backward or forward. “I commune with my own heart,” says David. The heart can never be kept—until its case be examined and understood
~John Flavel~
Keeping the Heart (Portland, Oregon; MonergismBooks.com; 2010) eBook. Section: What is Keeping the Heart?
The Old Guys 
Great thoughts!
How important for us today – to remember and to preach!
Keep on doing this good work!