John Calvin Commentary Psalms 40:10

"I have not hid thy righteousness within my heart; I have declared thy faithfulness and thy salvation; I have not concealed thy lovingkindness and thy truth from the great assembly." — Psalms 40:10 (ASV)

I have not hidden your righteousness within my heart. Here it is necessary to observe the accumulation of terms that are employed to denote the same thing. To the righteousness of God the Psalmist adds His truth, His salvation, and His mercy. And what is the purpose of this, but to magnify and set forth the goodness of God by many terms or expressions of praise?

We must, however, notice how these terms differ; for in this way we may be able to determine how they apply to the deliverance of which David here speaks. If these four things are taken in their proper order, mercy will hold the first place, as it is by mercy alone that God is moved to regard us.

His righteousness is the protection by which He constantly defends His own people, and the goodness by which, as we have already said elsewhere, He preserves them. And, so that no one may doubt that it will flow in a constant and uninterrupted course, David adds in the third place truth; by which we are taught that God always remains the same, and never tires of helping us, nor does He at any time withdraw His hand.

At the same time, this implies a presentation of the promises; for no one will ever rightly take hold of the righteousness of God unless he embraces it as it is offered and presented in the Word. Salvation is the effect of righteousness, for God continues to show His free favor to His people, daily giving them aid and assistance, until He has completely saved them.