The vine was always Israel, do a word search for VINE . The vine was uprooted from Egypt to the land of Israel. When Israel is referred to as the vine it is never good. Jesus says that he is the true vine, he is the Israel of God who will obey God the Father perfectly, the branches are Israel. There is no mention of the branches being grafted into the vine, so these branches grew with the vine. This passage of scripture is about Jesus and Israel not gentiles because gentiles are the body of christ and grafted into the olive tree. This passage is about Jewish disciples who stopped believing or stopped walking with him, Notice this passage is about the little flock Jesus is discoursing with his 11, he hasn't died yet and the holy spirit has not been given, gentiles are not granted repentance till Acts 10 and 11. This is not about gentile believers losing salvation at all. Its about unbelieving Israel's being cut off Romans 11:24 Read Ezekiel 15. There is so much in this passage to exegesis, Jesus tells them that they are clean through the word that I have spoken to you, Jesus in John 6 Jesus tells the 12 will you also leave Peter says you have the words of eternal life , John 8 he says my words do not abide in you. 1 Peter 2:3, Ephesians 5:26. Pray this helps God bless your studies