John Gill Commentary Psalms 63:9

"But those that seek my soul, to destroy it, Shall go into the lower parts of the earth." — Psalms 63:9 (ASV)

But those [that] seek my soul to destroy it
Meaning his life; for as for his soul, that was immaterial and immortal, and could never be destroyed by man: but as for his natural life, his enemies laid snares for that, and sought to take it away, and nothing less would satisfy them;

shall go into the lower parts of the earth ;
not the grave, where the righteous go as well as the wicked; besides, by their being the portion of foxes, as follows, it seems that they should have no burial; but hell is meant, the bottomless pit. Some take it to be a prayer, as Kimchi and Ben Melech; "may they go", or "let them go" see (Psalms 55:15) . The allusion may be thought to be to the death of Korah and his company.