John 8:35

And the servant abideth not in the house for ever: but the Son abideth ever.

A bondservant doesn't live in the house forever. A son remains forever.

And the bondservant abideth not in the house for ever: the son abideth for ever.

and the servant doth not remain in the house -- to the age, the son doth remain -- to the age;

A slave is not a permanent member of the family, but a son belongs to it forever.