(Devarim 3:24) "Your greatness (gadlecha)": His attribute of goodness, as in (Bamidbar 14:17) "And now, let the power (of goodness) of the L-rd be magnified ("yigdal") … as You have spoken (18) The L-rd withholds wrath and He is abundant in lovingkindness." This is the prototype for all "gadlecha" in the Torah. (Ibid.)
"and Your mighty hand": These are the ten plagues that the Holy One Blessed be He brought upon the Egyptians in Egypt, viz. (Shemoth 8:1) "Stretch forth your hand, etc."
(Ibid.) "For who is Almighty in the heavens and in the earth": For not as the measure of flesh and blood is that of the Holy One Blessed be He: The measure of flesh and blood: A governor sits on his seat, fearing that his counselors will overrule him. But You, who have no counselors (to overrule You), why don't You pardon me! An officer sits at his station, fearing that his commander will overrule him. But You, who have no commander, why don't You pardon me!