This is a Psalm of remembrance and of anticipation. That the right hand of the Lord has done valiantly is history. But it is also prelude. And singing it implies that we are thankful for God's past deliverance and that we are looking for God's future salvation.
We have been saved by Jesus' death and resurrection.
We are being saved by the Holy Spirit's continuing work in our hearts.
We will be saved on the Great Last Day when Jesus returns and takes his own to be with him in heaven.
Until that day we sing our praise to God for his past blessings, and in anticipation of even greater things to come!
