It begins, “The Lord is my light and my salvation.”
Salvation is perhaps not the best English word, not because it is not an accurate rendering of ישעה (yeshuah), but because “salvation” has so many false connotations in popular religion. Salvation does not mean “afterlife” specifically or an experience of religious change (conversion).
JPS translates “my help,” perhaps seeking to avoid this confusion. “My rescue” would probably have been better.
What does David mean by “the Lord is my rescue”? Surely David knows that we are not always rescued in every situation. The options include:
(1) David naively thinks he will be rescued from every adversity.
(2) David thinks God would rescue him from every adversity unless he sins (or lacks faith).
(3) David understands “rescue” has many dimensions and is God’s ultimate plan even if temporary adversity is allowed.
I think the third option is most likely. Adversity happens on God’s watch. But the God who watches adversity happen to us is our rescue. What form that rescue will take is sometimes beyond knowing. David had, at best, only a vague notion of rescue beyond death. But he trusted the rescuer even when not knowing how rescue was possible.