John Gill Commentary Deuteronomy 7:17

"If thou shalt say in thy heart, These nations are more than I; how can I dispossess them?" — Deuteronomy 7:17 (ASV)

If you should say in your heart
meaning if secret thoughts arise in the heart, misgivings of heart, fears and doubts there, which, though not outwardly expressed, might be inwardly retained:

these nations are more than I ;
seven to one, and perhaps anyone of them as powerful as Israel:

how can I dispossess them ?
of the land they inherit, and take possession of it.