Radak on Psalms
LET US GO: This is what Israel is saying to each other in the days of the Messiah, to sing to the Lord that redeemed them. And we have already explained that “lechu” are words of ziruz (alacrity/enthusiasm) in the action, not literally walking.
Metzudat Zion on Psalms
It is a language of action! Based on Genesis 37:20 “Let us go and kill them.” And [the verse continues to explain that] nariah is similar to teruah, to blow a horn.