Hear thou, my son, and be wise, and guide thine heart in the way.
Proverbs 23:19 (KJV)
We have control over what goes into our hearts. We are able to guide our hearts by taking charge over our thinking, and by being selective about what we pay attention to. What is in our hearts is determined by our predominant thoughts and by what comes in through our eyes and ears. The more that our thinking revolves around the Word of God, and the more we pay attention to what God is seeking to do in our lives, the more will our hearts be filled with the things of God.