Charles Ellicott Commentary Psalms 110:5

"The Lord at thy right hand Will strike through kings in the day of his wrath." — Psalms 110:5 (ASV)

The Lord at thy right hand. —We are naturally tempted to understand this as still referring to the king whom the first verse placed at Jehovah’s right hand. But the word for Lord here is Adonai, which is nowhere else used except in reference to God. Moreover, God throughout has so far appeared as the active agent. It is He who stretched out the sceptre and conferred the office of priest; and until now the king has been the person addressed.

It is therefore necessary still to consider him as addressed, and to suppose that Jehovah’s change of position from the king’s right hand to his left is simply due to the usage of the language. To sit at the right hand was an emblem of honour; to stand at the right hand was a figure of protecting might (Psalms 16:8; Psalms 109:31); and the imagery of a battle into which the song now plunges caused the change of expression.