Sforno on Deuteronomy 7:9/ספורנו על דברים ז׳:ט׳

1 הא-ל הנאמן, Who is constant, not subject to change.

2שומר הברית ומשלם לשונאיו, the meaning of the words רשע וטוב לו, [a favourite argument of the heretics who point to the afflictions suffered by the pious and the good life enjoyed by the pious in this life. Ed.] can be understood on two levels: 1) the “good” the wicked appear to enjoy in this life is due to merits accumulated by their forefathers who had not been recompensed for these as yet by G’d. A prominent example of this is the enjoyable life lived by Ishmael who benefited by Avraham’s merits. G’d Himself referred to this in Genesis 21,13 when He said כי זרעך הוא, “because he is your seed. 2) The wicked person himself has accumulated some merits; seeing that on balance he does not qualify for life in the hereafter, G’d has to compensate him while he is on earth. This He does by letting him enjoy the transient joys available in this life to the extent his merits entitle him to.