This is a phrase that I came upon in the early days of my Christian walk. It seemed strange to me then, but after walking with the Lord for the better part of four decades, I more fully understand why a "divided heart" is something to be guarded against.
I have rarely recommended a movie, frankly because the vast majority of them are spiritually defiling, but there is a film from several years back entitled "Time Changers", starring Gavin McLeod, that, in my opinion, is well worth watching. The premise of the movie is that a Christian scientist from the 1800s invents a time machine and is transported to modern time.
There is very obvious "culture shock" as the ungodliness of modern living is encountered- even in the church! It is very eye-opening as the viewer is brought face-to-face with issues that modern society has become comfortable with. There is one particular scene where the visitor from the past flees from a movie theater, where he has gone as part of a church outing, totally shocked that there was open blasphemy, taking the Lord's Name in vain, being spoken in the film.
A divided heart rapidly loses awareness of the "wrongness" of such things. After all, such is just a part of life in 2010. Is it any wonder that God tells us to keep our heart with all diligence.
Friend, how is it with your heart today? Would you be inclined to flee evil, as our fictional friend from the past did? Or, would you sit, munching popcorn, wondering what was wrong with this "religious nut"?
I can answer for no one but myself, but I think the ability to be shocked, embarrassed, and made to feel uncomfortable in the presence of that which offends the Lord is a healthy attitude of heart that ought to be nurtured.
Jesus said it best of all: "No man can serve two masters...". May we choose wisely.
God Bless