John Gill Commentary Exodus 15:5

"The deeps cover them: They went down into the depths like a stone." — Exodus 15:5 (ASV)

The depths have covered them
The depths of the sea covered Pharaoh and his host, so as to be seen no more; and in like manner will mystical Babylon, or antichrist, be destroyed, and be no more found and seen; as likewise the sins of God's people, being cast into the depths of the sea, and covered with the blood of Christ, will be seen no more; when they are sought for, they shall not be found: they sunk into the bottom as a stone ;
into the bottom of the sea, as a stone thrown into anybody of water sinks and rises not up again; this circumstance is observed by (Nehemiah 9:11) their persecutors thou threwest into the deep, as a stone into the
mighty waters ;
and thus a stone like a millstone being taken by an angel and cast into the sea, is made an emblem of the irrecoverable ruin and destruction of Babylon, or antichrist, (Revelation 18:21) .