Because your love is better than life, my lips will glorify you.
He can't help it. God's love is so amazing, so much better than anything this life has to offer, so far beyond life itself, that he cannot contain himself. His mouth pours out glory to the most amazing thing that he knows.
Many times what we love the most is what we talk about the most. It is like there is this connection between our mouth and our heart. Jesus even tells us that, "...out of the overflow of the heart, the mouth speaks."
If you want to know where your treasure is, ask yourself what you talk about the most.