I'm curious if you understood all of John. There is a key phrase that is in your quote in John 6. It has been misapplied to all believers, but it isn't. The phrase is "He has given Me." When those words are used, John is referring to His predestined apostles. After that he talks of those who believe their words.
I'm sure your denominations uses this next one to base their OSAS on. But if you open your spirit you will plainly see it refers to the apostles, except Judas.
John 10:
28 And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of My hand. 29 My Father, who has given them to Me, is greater than all; and no one is able to snatch them out of My Father’s hand. 30 I and My Father are one.”
John 17:
“I have manifested Your name to the men whom You have given Me out of the world. They were Yours, You gave them to Me, and they have kept Your word. 7 Now they have known that all things which You have given Me are from You. 8 For I have given to them the words which You have given Me; and they have received them, and have known surely that I came forth from You; and they have believed that You sent Me.
9 “I pray for them. I do not pray for the world but for those whom You have given Me, for they are Yours. 10 And all Mine are Yours, and Yours are Mine, and I am glorified in them. 11 Now I am no longer in the world, but these are in the world, and I come to You. Holy Father, keep through Your name those whom You have given Me, that they may be one as We are. 12 While I was with them in the world, I kept them in Your name. Those whom You gave Me I have kept; and none of them is lost except the son of perdition, that the Scripture might be fulfilled.
Not everyone is predestined either. Israel was predestined to be God's chosen people, but we know that doesn't mean they will all obey and be saved. That destroys another myth on the doctrine of predestination of all believers, calling them His elect. And out of Israel, it is the apostles that first believed that are also predestined, and given to Jesus by the Father.
Isaiah 45:4
For Jacob My servant’s sake, And Israel My elect, I have even called you by your name; I have named you, though you have not known Me.
Ephesians 1:
Blessed be the God and Father of our Lord Jesus Christ, who has blessed us with every spiritual blessing in the heavenly places in Christ, 4 just as He chose us in Him before the foundation of the world, that we should be holy and without blame before Him in love, 5 having predestined us to adoption as sons by Jesus Christ to Himself, according to the good pleasure of His will, 6 to the praise of the glory of His grace, by which He made us accepted in the Beloved. 7 In Him we have redemption through His blood, the forgiveness of sins, according to the riches of His grace 8 which He made to abound toward us in all wisdom and prudence, 9 having made known to us the mystery of His will, according to His good pleasure which He purposed in Himself, 10 that in the dispensation of the fullness of the times He might gather together in one all things in Christ, both which are in heaven and which are on earth—in Him. 11 In Him also we have obtained an inheritance, being predestined according to the purpose of Him who works all things according to the counsel of His will, 12 that we who first trusted in Christ should be to the praise of His glory.