The grammar does not agree with John Reese. τοῦτό (this) is a demonstrative pronoun functioning as the subject of the dependent clause. The only word that modifies τοῦτό is the conjunction ἵνα (that) making it a conjunction to pronoun relationship. Basically the sentence goes grammatically as the work of God is this, that you believe.......
This was an answer to the question: What must we do to do the work of God. The work of God is that you must believe. And this is exactly how they understood Jesus, and I think they probably knew Greek too.
Otherwise Jesus would have been asking them to do something that they in fact don't do, but God does.
So if the work of believing is God doing the believing then God is in fact believing in Himself. Which is nonsense.
Here is a simple way to put this to the test:
Luke 8:11 “Now the parable is this: The seed is the word of God. 12 Those by the wayside are the ones who hear; then the devil comes and takes away the word out of their hearts,
lest they should believe and be saved. 13 But the ones on the rock
are those who, when they hear, receive the word with joy; and these have no root,
who believe for a while and in time of temptation fall away. 14 Now the ones
that fell among thorns are those who, when they have heard, go out and are choked with cares, riches, and pleasures of life, and bring no fruit to maturity. 15 But the ones
that fell on the good ground are those who, having heard the word with a noble and good heart, keep
it and bear fruit with patience.
How is it that some can believe for awhile, when believing is "the work of God" or "a gift of God". How then can it fail? Be careful with your answer since:
John 6:44 No one can come to Me unless the Father who sent Me draws him; and I will raise him up at the last day. 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.”
and
John 10:26 But you do not believe, because you are not of My sheep, as I said to you. 27 My sheep hear My voice, and I know them, and they follow Me. 28 And I give them eternal life, and they shall never perish; neither shall anyone snatch them out of My hand.
So how is it then that some believe the word of God for awhile?