וַיִּגְדַּ֖ל הָאִ֑ישׁ וַיֵּ֤לֶךְ הָלוֹךְ֙ וְגָדֵ֔ל עַ֥ד כִּֽי־גָדַ֖ל מְאֹֽד׃
און דער מאַן איז געװאָרן רײַך, און איז נאָכאַנאַנד רײַכער געװאָרן, ביז ער איז געװאָרן זײער רײַך.
Rashi
כי גדל מאד UNTIL HE BECAME VERY GREAT — so that people used to say, “Rather the dung of Isaac’s mules than all Abimelech’s gold and silver’’(Genesis Rabbah 64:7).
Malbim
The man prospered. Scripture attributes this prosperity to Yitzchok’s own merit rather than to the bounty of the land. He continued to prosper. He never suffered a setback, which demonstrated that his prosperity was not by chance. Until he became very great. If his prosperity had been the result of favorable circumstances it would have reached a limit and then been followed by a downturn.