nigh: i.e. nigh to help. Compare Psalms 34:18; Psalms 119:151.Deuteronomy 4:7.
unto all. Note the Figure of speech Anadiplosis (App-6) in the repetition, "to all that call" (for emphasis).
Related Commentaries of Psalms 145:18
Psalms 145:18
18 The LORD is nigh unto all them that call upon him, to all that call upon him in truth.