It is not written "Mine is revenge and I shall pay," but "Mine is revenge and payment." I pay for their deeds and for the deeds of their fathers before Me, as it is written (Isaiah 65:6-7) "I will repay into their bosom, your sins and the sins of your fathers together … and I will mete out (payment for) their deeds first into their bosom."
"at the time their foot gives way": viz. (Isaiah 26:6) "The foot will tread it down, the foot of the poor one (the Messiah), the soles of the (heretofore) impoverished ones (Israel)." (Devarim, Ibid.) "For near is the day of their calamity": R. Yossi said: If of those of whom it is written "For near is the day of their calamity" — their punishment is being delayed, then of those of whom it is written (Isaiah 24:22) "and after many days they (their sins) will be remembered," how much more so!