In other words, when I read Rom 11:17-24, I don’t only stop with those being grafted into the vine freely by grace through faith (although strictly speaking there is nothing here about people freely grafting themselves into the vine). Those who are rejected for rejecting the stumbling stone, have by their rejection of the stone led to the reconciliation of the whole world and their own eventual acceptance in life out from the dead ones; for if the first piece of bread be holy, so shall the lump; and if the root is holy, so shall the branches be. Nor are we to disregard those who have been grafted out of the vine, for God can and will graft them back in again, just as God has grafted us in (and without violating our free will in any intolerable way) – and if we are not kind to those outside the vine, graft us back out again!
Consequently (going on past verse 17), I am no longer uninformed about this mystery, that a partial hardening has happened to Israel until the fulness of the Gentiles has come in, and thus all Israel will be saved from their sins at last, just as was written in the prophets: from the standpoint of God’s choice, they are beloved for the sake of the fathers, for the gifts and the calling of God are irrevocable. They did not stumble so as to fall; neither have the Gentiles; but God has imprisoned all into disobedience that God might show mercy to all: for from Him and through Him and to Him are all things!
The surety of salvation (not necessarily from punishment, but from sin) is preached just as much as the scope of salvation from sin in Romans 11.
No doubt (as you reference from John 15:1-7), those who removed from the Vine will be burned. But Paul warned us not to give up hope on them; and Jesus did, too, in His own way, for He issued this warning to the apostles themselves, that those who do not keep His commands and who do not bring forth much fruit are not loving Him. This command must (at the least) include the “new commandment” Christ already gave them earlier in this discourse (13:34-35) about loving each other as Christ loves them, by which people would know that they are His disciples, and which Christ reminds them of again here (15:12-14), “This is My precept, that you be loving one another in accord with how I love you” etc. Christ also reminds them that no man has greater love than to lay down his life for his friends; yet Christ has already told them long ago (during the Sermon on the Mount) that He expects them to love their enemies and sacrifice themselves for the sake of their enemies – which Christ Himself is about to do! Similarly at that time Christ wryly observed that if they do good only for each other, what more are they doing than pagans and traitors!? (Matt 5:38-48)
What then is the new commandment? To love their enemies, too, as Christ loves them and will not stop loving them once they become His enemies later that night. That means loving Judas Iscariot, too, who had departed to betray Jesus a little earlier that night (though no one but Jesus and the Beloved Disciple know this yet).
God’s love is greater than merely human love, for (as Paul says in Romans 5) hardly anyone would dare to die for a good man, but Christ showed God’s true love by coming and dying for us while we were yet sinners. Apostles who loved Judas Iscariot self-sacrificially would be staying in Jesus’ love and would be loving one another in a new way that the world would not conceive of by itself, the way Jesus loves them. But apostles who do not self-sacrificially love Judas Iscariot are under the same warning as what happens to Judas: being thrown out to be burned! Yet by the same token to interpret such a burning as hopeless would be for them to refuse to love their errant brother. St. Paul in Romans 11, in applying the same metaphor, emphatically insists that those who are currently grafted into the Vine should not be hopeless for those who are currently grafted out of the Vine, for God can graft in and out as He wishes and can graft back in whomever He has grafted out!–and can graft out those who insist on disparaging those who are currently grafted out!
Combined with Jesus’ remarks that those who bear little fruit (expecting evangelism to be few) are not remaining in Jesus’ love, the contexts add up to a warning against expecting hopeless punishment.
Relatedly, at the start of the High Priestly Prayer at the end of this discourse, 17:1-2, Jesus starts by praying, “Glorify Your Son, that the Son may glorify You; just as You gave Him authority over every flesh, so that He may give eonian life to everything You have given Him.”
By those explicit terms, the only way that the Son and the Father may glorify each other is if the Father gives all authority to the Son so that the Son may give eonian life to everything over which He has authority. That’s the context in which Jesus says He isn’t praying for the world but for His immediate disciples: He’s asking that they should be preserved as witnesses to the world, but it’s still the same principle because everything the Father gives the Son belongs to both Persons and must not be finally lost.
By the same token, this means that although the “son of perdition” given to the Son to be guarded will perish, so that the Scripture may be fulfilled, he still was also given to the Son and so shall not be finally lost; Judas isn’t among those whom Christ is praying will stay true for evangelizing the world, but he is among all those over whom the Son has been given authority for the purpose of giving them eonian life. “To Him be the glory into the eons amen!”