Charles Ellicott Commentary Psalms 36:5

"Thy lovingkindness, O Jehovah, is in the heavens; Thy faithfulness [reacheth] unto the skies." — Psalms 36:5 (ASV)

Thy mercy, O Lord, is in ... —Better,

Jehovah, to the heavens reaches Your grace,
Your faithfulness to the sky.

i.e., there are no narrower bounds of divine mercy and truth.