The LORD is longsuffering, and of great mercy, forgiving iniquity and transgression, and by no means clearing the guilty, visiting the iniquity of the fathers upon the children unto the third and fourth generation.
All Commentaries on Numbers 14:18 Go To Numbers 14
Jerome
AD 420
That is to say, God will not punish us at once for our thoughts and resolves but will send retribution upon their offspring, that is, upon the evil deeds and habits of sin which arise out of them.