John Gill 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 beseech you, the iniquity of this people ,
according unto the greatness of your mercy
Intimating, that though the sin of this people was great, the mercy of God to pardon was greater; and therefore he entreats that God would deal with them, not according to the greatness of their sins, and the strictness of justice, but according to the greatness of his mercy, who would, and does, abundantly pardon;

and as you have forgiven this people from Egypt even until now ;
which shows both that these people had been continually sinning against the Lord, ever since they came out of Egypt, notwithstanding the great goodness of God unto them, and that he had as constantly pardoned; and therefore it was hoped and entreated that he would still continue to pardon them, he being the same he ever was, and whose mercy and goodness endure for ever: he had pardoned already sins of the like kind since their coming out of Egypt, as their murmurings for bread in the wilderness of Sin, (Exodus 16:1–7) , and for water at Rephidim, (Exodus 17:1–7) , and even a greater sin than these, idolatry, or the worship of the calf, (Exodus 32:1–10) .