In Psalm 6:5 David protests to God: “For there is no mention of you in death; in Sheol who will give You thanks?” He is objecting to his potential death, saying in effect, what good would that do? One might submit that there IS remembrance and praise of God after death — we will worship Him in heaven forever! But perhaps David’s point here is that God would not be praised by him PUBLICLY, where people could see and hear and benefit from the testimony of his praise. This serves to remind us that one of the functions of our praise and thanks here on earth is to witness to OTHERS how great our God is.
This must be why in several places the Psalms talk about giving thanks and praising God “in the congregation”: Psalm 35:18, “I will give You thanks in the great congregation” (see also: 40:9, 10, 68:26, etc.) In other words, he was praising God publicly. It is important that we glorify God in ways which witness to other people. Some of us tend to want to make our praise of God a private matter only. This vertical aspect of our relationship with God is essential, and is good as far as it goes. But if that is all we ever do here on earth, then we might as well be in heaven praising God for all the good that we are doing others!
This should cause each of us to ask ourselves: how am I glorifying God publicly? Does He really have any good reason for leaving me here on earth, or would I praise Him just as well from the grave?