Rashi on Deuteronomy 7:9/רש"י על דברים ז׳:ט׳

1לאלף דור TO A THOUSAND GENERATIONS — But elsewhere (5:10) it states: to thousands of generations! The explanation is: Here where it is connected with (refers to) "those who keep His commandments" it states that God's grace is extended to a thousand generations; but there where it is associated with "those who love Him" it states that it is extended to thousands of generations (Sotah 31a);

2לאהביו are those who do the commandments out of love.

3ולשמרי מצותיו are those who do them out of fear.