John Calvin Commentary John 4:24

"God is a Spirit: and they that worship him must worship in spirit and truth." — John 4:24 (ASV)

God is a Spirit. This is a confirmation drawn from the very nature of God. Since humans are flesh, we should not be surprised if they take delight in those things that correspond to their own nature. This is why they devise many things in the worship of God that are full of display but have no substance.

But they should first of all consider that they are dealing with God, who can no more agree with the flesh than fire with water. This single consideration, when the question concerns the worship of God, should be sufficient to restrain the unruliness of our minds: God is so far from being like us that those things which please us most are objects of his loathing and abhorrence.

And if hypocrites are so blinded by their own pride that they are not afraid to subject God to their opinion, or rather to their unlawful desires, let us understand that this humility is of considerable importance in the true worship of God: to regard with suspicion whatever is gratifying according to the flesh.

Besides, since we cannot ascend to the height of God, let us remember that we should seek from His word the rule by which we are to be governed. This passage is frequently quoted by the Fathers against the Arians to prove the Divinity of the Holy Spirit, but it is improper to strain it for such a purpose. For Christ simply declares here that his Father is of a spiritual nature and, therefore, is not moved by frivolous matters, as people, through the fickleness and instability of their character, tend to be.