A.T. Robertson Commentary John 8:35

"And the bondservant abideth not in the house for ever: the son abideth for ever." — John 8:35 (ASV)

The bondservant (ο δουλος)...

the son (ο υιος). There is a change in the metaphor by this contrast between the positions of the son and the slave in the house. The slave has no footing or tenure and may be cast out at any moment while the son is the heir and has a permanent place. Cf. Ishmael and Isaac (Genesis 21:10) and Paul's use of it in Ga 4:30. We do not know that there is any reference here to Hagar and Ishmael. See also Heb 3:5 (Numbers 12:7) for a like contrast between Moses as servant (θεραπων) in God's house and Christ as Son (υιος) over God's house.