Keep your heart with all diligence, for out of it spring the issues of life.
The Bible teaches us that God will strengthen our hearts, fill our hearts with His peace, and purify our hearts, to name just a few of the blessings that the Lord promises to those who follow Him. But notice that we are told here that it's our responsibility to keep, or guard, our hearts. And we are told to do so "with all diligence."
It's in our hearts that our motives, our desires, and our priorities reside. This is where the fuel that defines who we are is ignited.
If we are really good at practicing outward self-control, the sin in our hearts may not be evident to others, but if lust, bitterness, or deceitfulness is alive and kicking in my heart, then a lustful, bitter, liar is what I am. Only by inviting Jesus in to renew our hearts can we be changed.
Knowing this, what do I want to allow to reside in my heart? If it's His Spirit, and love for the Lord and His word, then peace, truth, wisdom, and real love will live there.
Let's guard our hearts well, recognizing that our true treasure, Jesus Christ, must be given room to reign within us. We guard, He works, and the Living Water of the Lord will spring up and flow from our lives like never before.