John Wesley on Numbers 14:17

Be great - That is appear to be great, discover its greatness: namely, the power of his grace and mercy, or the greatness of his mercy, in pardoning this and their other sins: for to this the following words manifestly restrain it, where the pardon of their sins is the only instance of this power both described in God's titles, Nu 14:18, and prayed for by Moses Nu 14:19, and granted by God in answer to him, 14:20. Nor is it strange that the pardon of sin, especially such great sins, is spoken of as an act of power in God, because undoubtedly it is an act of omnipotent and infinite goodness.