Ramban: 'You will know from Yetzi'as Egypt a. that Hashem ... is the G-d who created Heaven and earth, ¹ and b. that He is true to His word, to adhere to the B'ris and the Chesed ... to their descendants just as He adhered to the B'ris that He made when He swore to take their children out of Egypt.'

Rashbam, Da'as Zekenim (on Pasuk 7), Hadar Zekenim (on Pasuk 7) and Moshav Zekenim: 'You will know that Hashem will fulfill His promise to the Avos to give the land to their children, but only to a worthy generation, ² for which He will wait up to a thousand generations - for a generation that loves Him and keeps His Mitzvos'.

Targum Yonasan: 'You will know that Hashem is a moghty and trustworthy Judge (who is capable of rewarding those who do His will and of punishing those who transgress it - Oznayim la'Torah) ... '.

Rashi: Bearing in mind that "Shomrei Mitzvosav" refers to those who serve Hashem out of fear, here, where the number is juxtaposed to those who serve Hashem out of fear, Hashem rewards up to one thousand generation, whereas in the earlier Pasuk, where the Torah juxtaposes the reward to those who serve Him out of love, the reward goes up to two thousand generations. ¹

Targum Onkelos and Targum Yonasan: In spite of the different wording, both Pesukim translate as 'for thousands of generations'.

Above, it says that two thousand generations receive reward. Here, it says that Hashem will fulfill His promise to the Avos within a thousand generations (refer to 7:9:1:2

Rashi: "Ohavav" refers to people who serve Hashem out of love, and "Shomrei Mitzvosav", to people who serve Him out of fear. ¹