John Gill Commentary 1 Kings 8:39

"then hear thou in heaven thy dwelling-place, and forgive, and do, and render unto every man according to all his ways, whose heart thou knowest; (for thou, even thou only, knowest the hearts of all the children of men;)" — 1 Kings 8:39 (ASV)

Then hear you in heaven your dwellingplace Which was more properly so than this Solomon had built, and the Lord had taken possession of:

and forgive ; remove the calamity and distress, be it what it may:

and do, and give to every man according to his ways, whose heartyou know : that his prayer is cordial and sincere, his confession and repentance genuine, and that he is truly sensible of his sin, and sorry for it, and is pure in his intentions and resolutions, through divine grace, to depart from it for the future:

(for you, [even] you only know the hearts of all the children ofmen; ) he knows all men, the hearts of them all, what is in them, what comes out of them, and is according to them; omniscience belongs only to God; it is his prerogative to know the heart and search the reins, see (Jeremiah 17:9Jeremiah 17:10) .