There is only one way to interpret it and that is by believing what you read. Look at this explanation by John. Keep in mind that when he writes his gospel in 90 AD, it is in retrospect and his understanding of the ministry of Jesus Christ is far greater than when he lived out these details he put in his gospel. He writes in the past tense, looking back. Note;
John 1:11 He came unto his own, and his own received him not.
12 But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name:
He wrote John 6 and was in the band of the 12 who did not know what it meant at the time to eat the flesh of the son of man in order to have everlasting life. He surely did know when he wrote his gospel and he knew how sinners became sons of God, which requires a birth into God's family through his son.
1 John 3:Behold, what manner of love the Father hath bestowed upon us, that we should be called the sons of God: therefore the world knoweth us not, because it knew him not.
2 Beloved, now are we the sons of God, and it doth not yet appear what we shall be: but we know that, when he shall appear, we shall be like him; for we shall see him as he is.
Now, for a definition or an equivalence of supper time that we found in Lk 14.
Gal 4:4 But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law,
5 To redeem them that were under the law, (that would be the circumcision) that we might receive the adoption of sons.
6 And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba, Father.
7 Wherefore thou art no more a servant, but a son; and if a son, then an heir of God through Christ.
The fullness of time (singular) was the end of a time and the beginning of another. Under the former time that had come to it's fullness, sinners could be a servant of God by keeping his law as a lifestyle but they could not be a son. Under the law of liberty, which Jesus Christ our Lord ushered in at his resurrection, men could be a son of God when they received the Spirit of Christ into their bodies by faith in his death, burial, and resurrection.
Rom 10:4 For Christ is the end of the law for righteousness to every one that believeth.
Ga 3:23 But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed.
24 Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith.
25 But after that faith is come, we are no longer under a schoolmaster.
26 For ye are all the children of God by faith in Christ Jesus
This is written to gentiles because Israel would not come. Who failed here? God? No, Israel failed and God wrote his history a different way than he would have.
Rom 10:1 Brethren, my heart's desire and prayer to God for Israel is, that they might be saved.
2 For I bear them record that they have a zeal of God, but not according to knowledge.
3 For they being ignorant of God's righteousness, and going about to establish their own righteousness, have not submitted themselves unto the righteousness of God.
The righteousness of God would be Christ. What glorious and wonderful truths God has given us. What a privilege for us gentiles to be accepted in the beloved. A saved man ought to shout right here.
