Albert Barnes Commentary Psalms 16:1

"Preserve me, O God; for in thee do I take refuge." — Psalms 16:1 (ASV)

Preserve me, O God - Keep me; guard me; save me. This language implies that there was imminent danger of some kind - perhaps, as the subsequent part of the psalm would seem to indicate, danger of death. See (Psalms 16:8–10). The idea here is, that God was able to preserve him from the impending danger, and that he might hope he would do it.

For in thee do I put my trust - That is, my hope is in you. He had no other reliance than God; but he had confidence in him - he felt assured that there was safety there.