Proverbs 3:1

My Son, do not forget my teaching, but let your heart keep my commandments; for length of days and years of life (worth living) and tranquility and prosperity they will add to you. 

What we keep our focus on is what has our attention. When we meditate on the Word, we keep our attention and focus on the direction of God. The direction enables us to keep on track and move forward with God without getting sidetracked by dead ends. It also helps us tune out the negative voices of the world.