Adam Clarke on Psalms 71:20

Thou, which hast showed me great and sore troubles - Multiplied straits and difficulties. And thou hast only showed them.

Hadst thou permitted them to have fallen upon me with all their own energy and natural consequences, they would have destroyed me. As it was, I was nearly buried under them.

Shalt quicken me again - Shalt revive me - put new life in me. This has been applied to the passion of our Lord, and his resurrection; for it is added, Thou: -

Shalt bring me up again from the depths of the earth - Death shall not prey upon my body; thy Holy One can see no corruption. As applicable to David, it might mean his being almost overwhelmed with afflictions; and his deliverance was like a life from the dead.