The Lord preserveth the simple; i.e. "the simple-minded"—those who are without guile or artifice (comp. Psalms 19:7). I was brought low. The same verb is used here as in Isaiah 38:14, where it is translated "fail" ("mine eyes fail").
It expresses extreme weakness, or exhaustion. And he helped me; or, "saved me" (comp. Isaiah 38:20).