Mercy shall be built up for ever - God's goodness is the foundation on which his mercy rests; and from that source, and on that foundation, acts of mercy shall flow and be built up for ever and ever.
Thy faithfulness shalt thou establish - What thou hast promised to do to the children of men on earth, thou dost register in heaven, and thy promise shall never fail.
For I have said - The Septuagint and the Latin Vulgate render this, “Thou hast said,” which is more in accordance with what the connection seems to demand; but the Hebrew will not admit of this construction. The true meaning seems to be, that the psalmist had said; that is, he had said in his mind; he had firmly believed; he had so received it as a truth that it might be spoken of as firmly settled, or as an indisputable reality. It was in his mind one of the things whose truthfulness did not admit of a doubt.
Mercy shall be built up for ever - The mercy referred to; the mercy manifested in the promise made to David. The idea is, that the promise would be fully carried out or verified. It would not be like the foundation of a building, which, after being laid, was abandoned; it would be as if the building, for which the foundation was designed, were carried up and completed. It would not be a forsaken, half-finished edifice, but an edifice fully erected.
Thy faithfulness shalt thou establish - In the matter referred to - the promise made to David.
In the very heavens - literally, “The heavens - thou wilt establish thy faithfulness in them.” That is the heavens - the heavenly bodies - so regular, so fixed, so enduring, are looked upon as the emblem of stability. The psalmist brings them thus before his mind, and he says that God had, as it were, made his promise a part of the very heavens; he had given to his faithfulness a place among the most secure, and fixed, and settled objects in nature. The sun in its regular rising; the stars in their certain course; the constellations, the same from age to age, were an emblem of the stability and security of the promises of God. Compare Jeremiah 33:20-21.