Albert Barnes Commentary Psalms 105:26

"He sent Moses his servant, [And] Aaron whom he had chosen." — Psalms 105:26 (ASV)

He sent Moses his servant – He sent Moses to be his servant in delivering his people; that is, to accomplish the work which he had designed should be done.

And Aaron whom he had chosen – whom he had selected to perform an important work in delivering his people from bondage.