John Gill Commentary Psalms 69:15

"Let not the waterflood overwhelm me, Neither let the deep shallow me up; And let not the pit shut its mouth upon me." — Psalms 69:15 (ASV)

Let not the water flood overflow me
The enemy, Satan, that came in like a flood upon him, with his whole posse of devils; or the wrath of God, which came upon him like a flood overwhelming him:

neither let the deep swallow me up :
as Jonah by the whale, and Dathan and Abiram in the earth:

and let not the pit shut her mouth upon me ;
either the pit of hell; so the Targum interprets it: for Christ, when he endured the curses of the law, and the wrath of God, suffered the same for kind as the damned in hell; only the mouth of this pit could not be shut upon him, or he be continued under such wrath and curse:

or else the pit of the grave, where his divine Father left him not, or suffered him to be so long in it as to see corruption; this pit was not shut upon him, but he was delivered out of it, and will die no more.