Our physical strength is clearly limited. Our mind too ~ when I use mine to solve a problem, I can only go so far. When I want to praise God, I run out of words to say. Now, when it comes to our heart, it knows no such bounds as it responds to the Lord directly. He can make us love him and others as much as he wants to with no cutoffs. If I yearn for God, he can increase that desire as much as he wishes. It's all up to him. A heart responding to God unites us to God, giving us unlimited power to change ourselves and the world.