Psalm 39: 1-6
I said to myself, " I will watch what I do and not sin in what I say. I will hold my tongue when the ungodly are around me." But I stood there in silence--not even speaking of good things--then turmoil within me grew worse. The more I thought about it, the hotter I got, igniting a fire of words: "Lord, remind me how brief my time on earth will be. Remind me that my days are numbered--how fleeting my life is. You have made my life no longer than the width of my hand. My entire lifetime is just a moment to you; at best, each of us is but a breath." We are merely moving shadows, and all our busy rushing ends in nothing. We heap up wealth, not knowing who will spend it.

David begins this chapter showing his humanity. He is talking about an inner monologue he has had about his temper and his tongue. How many times have we been in a position like this? Surrounded by co-workers, friends or even strangers and we were getting angrier by the minute but we had promised ourselves to be good and try to share God's word or at the last be nice but our response instead was nothing more than mere silence.
From this feeling, David goes into how fleeting life is. David is asking God to make him move. When he should have spoken, he was silent. David does not want that to happen again, for he is not guaranteed tomorrow so he wants to take full advantage of every opportunity today. As should we all.