And when He comes, He will reprove the world of sin, and of righteousness, and of judgment: Of sin, because they believe not on Me… – John 16:8,9

He that believeth on Him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God. – John 3:18

The all-seeing One, when He beholds men spurning the supreme gift of His love, cannot but regard such rejection as the worst proof of the hatred of their hearts against Himself. When the Holy Spirit comes to convince men of sin, the special sin which He brings to light is thus described, “Of sin, because they believed not on Me.” Not because the heathen were licentious in their habits, barbarians in their wars, and the bloodthirsty in their spirit. No, “Of sin, because they believe not on Me.”

Condemnation has come upon men, but what is the condemnation? “That light is come into the world, and men love darkness rather than light, because their deeds are evil.” Remember, also, that expressive text, “He that believes not is condemned already.” And what is he condemned for? “Because he has not believed in the name of the only-begotten Son of God.”

Let me remark, further, that in the rejection of divine mercy as presented in Christ, the unbeliever has displayed intense venom against God, for observe how it is. He must either receive the mercy of God in Christ, or he must be condemned—there is no other alternative. He must trust Christ whom God has set forth to be the propitiation for sin, or else he must be driven from the presence of God into eternal punishment. The unbeliever in effect says, “I had sooner be damned than accept God’s mercy in Christ.” Can we conceive a grosser insult to the infinite compassion of the great Father? ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/1012.cfm