John Calvin Commentary Numbers 14:19

"Pardon, I pray thee, the iniquity of this people according unto the greatness of thy lovingkindness, and according as thou hast forgiven this people, from Egypt even until now." — Numbers 14:19 (ASV)

Pardon, I plead with you, the iniquity of this people. In order to encourage his hope of pardon, he first considers the greatness of God’s mercy, and then the past instances by which it had been proved that God was inclined to forgive.

Indeed, the mercy of God continually invites us to seek reconciliation whenever we have sinned. Though iniquities heaped upon iniquities and the very enormity of our sins might justly make us afraid, still the abundance of His grace, which is mentioned here, must surely come to mind to swallow up all dread of His wrath.

David, also, resorting to this refuge, provides us an example of how all alarm can be overcome (Psalms 51:1). But since the bare and abstract recognition of God’s goodness is often insufficient for us, Moses applies another support in the shape of experience: Pardon, he says, as you have so often done before.

For since the goodness of God is unwearied and inexhaustible, the more often we have experienced it, the more we should be encouraged to implore it. This is not so that we may sink into licentious indulgence in sin, but so that despair does not overwhelm us when we are under God's condemnation and our own conscience strikes and torments us.

In short, let us regard this as a most effective method of earnest entreaty: when we appeal to God based on the benefits we have already experienced, asking that He will never cease to be gracious.