David personifies aspects of God's creation, especially things that appear in the heavens. The reason for this is because all of us, before conversion, have had some concept of God. For some of us religious folk, that concept was very fervently, sincerely believed and practiced. But for most of us, the concept of God was vague, maybe even agnostic, doubting. For others, their concept of God was atheistic, that there is no God. Whatever the case, for most, their concept of God is drawn from the creation. David is illustrating this here.
God's creation gives people a picture or an idea that God exists. They may be attracted by the beauty or the vastness they see in what God made, or it may be a combination of factors for their belief. David is showing that creation possesses its own eloquence. In the combination of its vastness, power, beauty, simplicity within complexity, etc., a person begins to think that there is more to life than himself, more than merely living out a span of time and then dying.
John W. Ritenbaugh
Unleavened Bread and Pentecost