‘And the slave does not remain in the house for ever, the son remains for ever. So if the Son makes you free, you will indeed be free'.
Jesus now contrasts those who are slaves to sin to those who become sons of God's household through the power and authority of the true Son. Those who are slaves have no permanent benefits. One day they will lose out. They have nothing permanent. (The Pharisees thought that they had a permanent place in God's household but they were wrong). But those who become sons because of their response to the Son become free from such slavery. They are made free by the Son. And their position in God's household is therefore permanent.
There are three ways in which we can interpret this sentence in depth. The first is to interpret it in detail. Thus it can be seen as saying that sin makes men slaves to their master Sin, as they serve in his household, while the Son makes men free sons in His household. The slave in ‘the household of sin', with sin as his master, can only be a loser. Any seeming benefits are temporary. Let those who enjoy sin recognise that it will let them down in the end. The sinner may think that he gets the best bargain but he only receives what is temporary, for as a slave he has no rights and no standing, and will one day be thrown out and will lose everything.
In contrast the one who receives sonship receives a permanent position. So the one who through breaking with sin by faith in Christ receives a place in ‘the household of God' and has permanent existence in that household. Thus if the Son makes men free, by bringing them into sonship, and removing them from the household of sin into the household of God, then their place in the household of God is eternal, not passing or fading away, and they are free indeed from the control of sin.
Alternately, the intention may have been to indicate the simple contrast of a temporary position in a household with a position of permanence, contrasting Isaac, the primary son, with Ishmael, the son of the slave girl, who was cast out. The idea then is that sin offers only what is temporary, while Jesus offers sonship, which is permanent, and gives total freedom (‘the house' not having any interpretative significance). Compare for this Paul's argument in Galatians 4:21-30.
Alternately ‘the son' might refer to Jesus in both cases, in which case the meaning is that sin only gives you what is temporary while the Son invites you to forsake sin and share His permanence, thus receiving freedom from sin which is true freedom. In the end the overall meaning is the same.