The church gathers to worship God receiving truths inherited from the past and expressing them in present contexts with a view to future hope.
From Michael Kelley:
During Joshua’s lifetime, the people worshiped faithfully, having their worship formed by their past. But they were only one generation away from forgetting all God had done, and therefore the Lord Himself. This is what happens when our worship is not rooted and formed by the past.
That does not mean we only sing old songs. But it does mean that when we sing, we sing with the aim of remembering old truths. We should care deeply about the substance of what we’re singing, for when we sing, we should always be recounting the old, old story of a Savior who came from glory. Who gave His life on Calvary to save a wretch like me. This is the greatest act of God. This is ultimately what all our worship should be rooted and formed by – recalling, remembering, and retelling the story of the gospel of Jesus Christ.
Our worship is formed by the past. But our worship shapes the present. Here’s what I DON’T mean by that – I don’t mean that we can somehow praise something into existence. That we can sing songs about victory and all our circumstantial problems will go away. This is not some name it and claim it worship methodology. What I mean is that when we sing, our understanding and perspective on the present is shaped.
Notice that verse 1 tells us that we should sing a new song to the Lord. This Psalm is part of a group of psalms that were sung to give praise to God as King. They’re sometimes called coronation psalms. And when these songs were sung at specific times in the calendar, there would be new songs composed.
That doesn’t mean that we need to write a new song every Sunday for worship; but it does bring a sense of freshness and present tense to worship. And we need our present to be formed by worship because we are emotional beings. God made us that way. The problem is that our emotions are corrupted by sin, just as every part of us is. That means that you cannot trust your heart, just like I cannot trust mine.