Let destruction come upon him at unawares; i.e. let the evil happen to him that he designed against others. As he sought to catch others in traps of which they knew nothing (Psalms 35:7), so let an unexpected destruction come upon him.
And let his net that he hath hid catch himself (comp. Psalms 9:15, Psalms 9:16; Psalms 57:6; Psalms 141:10). It is the perfection of poetic justice when "the engineer" is "hoist by his own petard." Into that very destruction lot him fall; rather, for destruction let him fall therein; i.
e. let him not only fall into his own trap, but let his fall prove his destruction. David's imprecations have always something about them from which the Christian shrinks; and this is particularly the case when he asks for his enemies' destruction.