John Gill Commentary Psalms 108:4

"For thy lovingkindness is great above the heavens; And thy truth [reacheth] unto the skies." — Psalms 108:4 (ASV)

For your mercy is great above the heavens. It is in (Psalms 57:10), "your mercy is great unto the heavens". (See Gill on Psalms 57:10).