Acts 7:6

God also told Abraham that his offspring would be slaves and suffer mistreatment outside their land for 400 years (Genesis 15:13), namely, from the year their enslavement began, evidently 1845 B.C., to the Exodus, 1446 B.C. Some interpreters take the 400 years as a round number. [Note: See also Harold W. Hoehner, "The Duration of the Egyptian Bondage," Bibliotheca Sacra 126:504 (October-December 1969):306-16.]

The Israelites were currently under Roman oppression but were about to lose their freedom and experience antagonism outside the land for many years. Jesus had predicted this (Matthew 23:1 to Matthew 25:46).