This is how God put it: his descendants would live as foreigners in a land not their own, and would be enslaved and mistreated for four hundred years.
In context
4So he left the land of the Chaldeans and settled in Haran. After his father died, God moved him from there into this land where you now live. 5He gave him no inheritance in it, not one foot of ground, yet he promised to give it to him as a possession, and to his descendants after him — and at the time he had no child. 6This is how God put it: his descendants would live as foreigners in a land not their own, and would be enslaved and mistreated for four hundred years. 7‘But I will judge the nation that enslaves them,’ God said, ‘and afterward they will come out and worship me in this place.’ 8And he gave him the covenant of circumcision. So Abraham became the father of Isaac and circumcised him on the eighth day; Isaac was the father of Jacob, and Jacob of the twelve patriarchs.