is not a permanent member
The phrase highlights the transient and insecure position of a slave within a household. In ancient times, a slave could be sold or transferred at the master's will, emphasizing the lack of permanence and security. This serves as a metaphor for the spiritual condition of those who are enslaved by sin; they do not have a lasting place in God's family. The temporary nature of a slave's position contrasts sharply with the eternal security offered to believers.

of the family
The "family" here refers to the household of God, a recurring theme in the New Testament that signifies belonging, relationship, and inheritance. In a biblical sense, being part of God's family means being in a covenant relationship with Him, enjoying the privileges and responsibilities that come with being His child. This familial language underscores the intimacy and love that God extends to those who are His.

but a son
The word "son" is translated from the Greek "υἱός" (huios), which signifies not just a male child, but an heir with full rights and privileges. In the cultural context of the time, a son had a permanent place in the family and was entitled to the inheritance. Spiritually, this represents believers who, through faith in Christ, are adopted into God's family and enjoy the full rights of sonship, including eternal life and a secure place in God's kingdom.

belongs to it forever
This phrase emphasizes the eternal security and permanence of the believer's position in God's family. The Greek word "μένει" (menei) means to remain or abide, indicating a lasting and unchangeable status. In contrast to the temporary status of a slave, a son has an unbreakable bond with the family. This assurance of eternal belonging is a cornerstone of Christian faith, offering hope and confidence to believers that their relationship with God is secure and everlasting.

The Son abideth ever.--Better, for ever, as in the earlier clause. The Greek words are precisely the same. This contrast between the position of the slave, who is a chattel that may be bought or bartered or sold, and has no affinity with the members of the house, and no permanent right in it; and the son, in whose veins is the master's blood, and who is heir of all things, is obvious and general; but here, again, the present meaning is special. They claim to be the seed of Abraham. Did they remember the history of Isaac and Ishmael? The son of the freewoman abideth in the house; the son of the bondmaid is cast out. Here, once again, too, we have the pupil of Gamaliel taking up and expanding this thought, showing that it was within the range of current exposition. Read carefully Galatians 4:19-31, remembering that the Epistle belongs to the middle of the half-century which separates the utterance of these words by Christ from their record by St. John.

The Greek word for "abideth" is the word which is rendered "continue" in John 8:31, and the Authorised version further obscures the connection by placing a paragraph division between these verses. If we read again John 8:31-32, noting the close connection between abiding, truth, and freedom; and the next verses, John 8:35-36, noting the connection between abiding, the Son, and freedom, we shall have, it is believed, a simpler clue to the meaning than any of the usual explanations.

Our version misleads by the use of the capital. The word "Son" in this verse, should be read "son." The clause is the expression of a legal maxim holding good for all servants and for all sons, but here specially applied to the sonship in Abraham's household. It is not before the next verse that there is the transference of thought to the Son in the household of the Divine Father. In this verse the thought is that if they were really the children of Abraham they would be of Abraham's spiritual nature, abiding in his home, and inheriting the promises made to him. They had not continued in the spiritual freedom of sons, but had departed from the house and had become, spiritually, bondmen. . . .