Much like a wrote about what we can choose to put on our feet; either choosing to focus on the care and decoration and glorification of our human bodies, or choosing to do something God glorifying in terms of spreading the gospel and being a blessing to others, so we have choices to make about what fills our mouthes.
Now, of course, I'm not talking about food. I'm talking about words. Althought, as someone who has had a life-long struggle with weight, I'm always touched by the irony of the fact that when you are on a diet, you are more concerned about what you are filling your mouth with than when you are gaining weight! You'd think that if you wanted to lose weight, you'd be trying NOT to think about what to eat, how much to eat and when you are going to eat again! And certainly, if we fill our mouths with the wrong things, we pay the price and that doesn't bring glory to God!
Think instead of the words that fill and come out of our mouths. Obviously, foul language, gossip and so on are to be avoided. Nobody is perfect, including me; I've lost my temper and slipped, and not just in the distant past! But think about the mindless banter that passes as communication in our world. Conversations about the sporting event the day before; discussions about American Idol (yeah, we're now just admitting right up front that we're promoting idolatry in this nation!), the Amazing Race and so on fill our ears and all too often our mouths! But God gave us that mouth and the brains to form and decode the complexities of language for a more noble purpose; to worship! Psalm 71:8 shows the author's intent to fill his mouth with praise, tellling of God's glory.
Obviously, none of us can live at that level of intensity where all we think and talk about is God and worshipping God and praying; that will come when we reach heaven. We all will engage in those conversations from time to time, or even more important ones with loved ones. But praise for God should always be in the back of our minds, ready to burst onto our lips!
71:8 My mouth is filled with thy praise, and with thy glory all the day.