Because it's not words Jesus spoke.
I post Scripture in blue and what Jesus said in red.
He does not predestinate those who believe. Rather, he foreknows and predestinates them so that they should believe.
Well, some Calvinists believe that.
The way I read the verse is that God foreknows who would accept His gift of salvation given the chance and then instead of sending them to hell for their sin as they still really do deserve. He decided to take them to heaven, so they those who believe are predestined for heaven.
It's a slightly different reading than usual but I don't see it in conflict with any other Scripture.
“Because it’s not words Jesus spoke”
Technically, Christ’s words ceased after “there were some of you that believe not.” and begin again at ‘Therefore I said unto you, no one can come unto me except it is given to him by my Father’ That’s why I thought maybe the “and” was trying to separate the cause and effect of that passage.
“The way I read the verse is that God foreknows who would accept His gift of salvation given the chance and then instead of sending them to hell for their sin as they still really do deserve.”
Check the order:
Jer_24:7 And I will give them an heart to know me, that I am the LORD: and they shall be my people, and I will be their God: for they shall return unto me with their whole heart.
Act_13:48 ... and as many as were ordained to eternal life believed.
Joh_15:16 Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and that your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you.
Rom_8:30 Moreover whom he did predestinate, them he also called: and whom he called, them he also justified: and whom he justified, them he also glorified.
There’s no “they believed, and therefore He ordained them.” And there is no “He called, and they justified themselves by their response, and therefore God predestinated them.” It’s “whom He did predestinate, them He also called; and whom He called, He justified” etc.