For thy mercy is great unto the heavens - See this explained in the notes at Psalm 36:5.

Thy mercy is great unto the heavens - It is as far above all human description and comprehension as the heavens are above the earth. See the notes on Psalm 36:5, Psalm 36:6, where nearly the same words occur.

For thy mercy [is] great unto the heavens, and thy truth unto the (k) clouds.
(k) Your mercies not only belong to the Jews, but also to the Gentiles.

For thy mercy is great unto the heavens,.... Which denotes the exceeding greatness and largeness of it; as it is in the heart of God, who is plenteous in mercy; as it is expressed in the covenant of grace, where are stores of it; as it is shown forth in the choice of persons to eternal life; in the mission of Christ into this world to die for them; in the regeneration of them, the pardon of their sins, and eternal life: and this mercy is not only extended to persons in the several parts of the earth, but is as high as the heaven above it, Psalm 103:11;
and thy truth unto the clouds; the faithfulness of God in performing his purposes and his promises; or the Gospel, and the doctrines of it, which contain the deep things of God; unless Christ himself should be meant, who is the truth which sprung out of the earth, Psalm 85:11; is now ascended unto heaven, and is higher than the heavens; and whose exaltation and glory may be designed in Psalm 57:11.