“He who does not believe God has made Him a liar: When we refuse to believe on Jesus, we reject the testimony God has given of His Son. Therefore, we call God a liar with our unbelief” (1 John 5:10).
Quoting Charles Spurgeon heavily, David Guzik, known for his verse by verse Bible commentary, writes the following comments on the above text:
John here exposes the great sin of unbelief. Most everyone who refuses to believe God (in the full sense of the word believe) doesn’t intend to call God a liar. But they do it nonetheless. “The great sin of not believing in the Lord Jesus Christ is often spoken of very lightly and in a very trifling spirit, as though it were scarcely any sin at all; yet, according to my text, and, indeed, according to the whole tenor of the Scriptures, unbelief is the giving of God the lie, and what can be worse?” (Spurgeon)
What if one says, “Well, I want to believe, but I can’t.” Spurgeon answers such a one: “Hearken, O unbeliever, you have said, ‘I cannot believe,’ but it would be more honest if you had said, ‘I will not believe.’ The mischief lies there. Your unbelief is your fault, not your misfortune. It is a disease, but it is also a crime: it is a terrible source of misery to you, but it is justly so, for it is an atrocious offense against the God of truth.”
What if one says, “Well, I’m trying to believe, and I’ll keep on trying.” Spurgeon speaks to this heart: “Did I not hear some one say, ‘Ah, sir, I have been trying to believe for years.’ Terrible words! They make the case still worse. Imagine that after I had made a statement, a man should declare that he did not believe me, in fact, he could not believe me though he would like to do so. I should feel aggrieved certainly; but it would make matters worse if he added, ‘In fact I have been for years trying to believe you, and I cannot do it.’ What does he mean by that? What can he mean but that I am so incorrigibly false, and such a confirmed liar, that though he would like to give me some credit, he really cannot do it? With all the effort he can make in my favour, he finds it quite beyond his power to believe me? Now, a man who says, ‘I have been trying to believe in God,’ in reality says just that with regard to the Most High… The talk about trying to believe is a mere pretence.
But whether pretence or no, let me remind you that there is no text in the Bible which says, ‘Try and believe,’ but it says ‘Believe in the Lord Jesus Christ.’ He is the Son of God, he has proved it by his miracles, he died to save sinners, therefore trust him; he deserves implicit trust and child-like confidence. Will you refuse him these? Then you have maligned his character and given him the lie.”