John 6, people make these choices to depart and follow demonic doctrines, but they do so because God was not working in their life as in them being born of God and being taught by the Holy Spirit.
35 And Jesus said to them, “I am the bread of life. He who comes to Me shall never hunger, and he who believes in Me shall never thirst. 36 But I said to you that you have seen Me and yet do not believe. 37 All that the Father gives Me will come to Me, and the one who comes to Me I will by no means cast out. 38 For I have come down from heaven, not to do My own will, but the will of Him who sent Me. 39 This is the will of the Father who sent Me, that of all He has given Me I should lose nothing, but should raise it up at the last day.
44 No one can come to Me unless the Father who sent Me draws him; and I will raise him up at the last day. 45 It is written in the prophets, ‘And they shall all be taught by God.’ Therefore everyone who has heard and learned from the Father comes to Me.
60 Therefore many of His disciples, when they heard this, said, “This is a hard saying; who can understand it?”
61 When Jesus knew in Himself that His disciples complained about this, He said to them, “Does this offend you? 62 What then if you should see the Son of Man ascend where He was before? 63 It is the Spirit who gives life; the flesh profits nothing. (you must be born again spiritually to follow Christ) The words that I speak to you are spirit, and they are life. 64 But there are some of you who do not believe.” For Jesus knew from the beginning who they were who did not believe, and who would betray Him. 65 And He said, “Therefore I have said to you that no one can come to Me unless it has been granted to him by My Father.”
66 From that time many of His disciples went back and walked with Him no more. 67 Then Jesus said to the twelve, “Do you also want to go away?”
68 But Simon Peter answered Him, “Lord, to whom shall we go? You have the words of eternal life. 69 Also we have come to believe and know that You are the Christ, the Son of the living God.”
The ones who remained came to believe and know because they were given to Christ by God, and they had been taught by the Holy Spirit to believe in Him.
Given to Christ also means they are born of God, so then part of His family, and God saves His children only, not anyone else, (here am I and the children whom God has given me Hebrews 2:10-13)