Predestination to His Salvation is not to all. That was shown in John 17 by our Lord's Prayer before He was delivered up.
John 17:6
6 I have manifested Thy name unto the men which Thou gavest Me out of the world: Thine they were, and Thou gavest them Me; and they have kept Thy word.
KJV
Jesus was talking about His Apostles and disciples at His first coming. They had belonged to The Father beforehand, and The Father gave them to Jesus.
John 17:14-18
14 I have given them Thy word; and the world hath hated them, because they are not of the world, even as I am not of the world.
15 I pray not that Thou shouldest take them out of the world, but that Thou shouldest keep them from the evil.
16 They are not of the world, even as I am not of the world.
17 Sanctify them through Thy truth: Thy word is truth.
18 As Thou hast sent Me into the world, even so have I also sent them into the world.
KJV
The idea of being 'sent' is specifically what the meaning of the word apostle is about.
Here's comes a dividing line between His sent ones, and others that would believe through their preaching of The Gospel:
John 17:20-21
20 Neither pray I for these alone, but for them also which shall believe on Me through their word;
21 That they all may be one; as Thou, Father, art in Me, and I in Thee, that they also may be one in Us: that the world may believe that Thou hast sent Me.
KJV
Not only did Jesus pray for His elect 'sent' ones which The Father owned beforehand and gave Him, but also... for those who would come to believe on Him through their word (preaching of The Gospel). And that purpose being that all in Christ Jesus might become one in Him and The Father.
By that we see the second group, those who would believe by the preaching of His 'sent' ones, were NOT predestined, owned beforehand, by The Father. For many are called, but few are chosen, like our Lord Jesus said.
This solves any mystery about predestination of Christ's elect servants. Predestination does not apply to all that have believed on Him. But those who believe by His 'sent' ones become PART of their elect status, which is why Apostle Paul would preach that all who have believed are part of the foundation ordained before the world began per Ephesians 2, etc.