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

What is a man’s warrant then for believing in Christ. Here it is. Christ tells him to do it, that is his warrant. Christ’s word is the warrant of the sinner for believing in Christ-not what he feels nor what he is, nor what he is not, but that Christ has told him to do it. The Gospel runs thus: “Believe on the Lord Jesus Christ and thou shalt be saved. He that believeth not shall be damned.” Faith in Christ then is a commanded duty as well as a blessed privilege, and what a mercy it is that it is a duty because there never can be any question but that a man has a right to do his duty…Now it is a command of God given to every creature that he should believe on Jesus Christ whom God hath sent. This is your warrant, sinner, and a blessed warrant it is, for it is one which hell cannot gainsay, and which heaven cannot withdraw…Now I need not say I am not fit to come for I am commanded to come, and I am threatened if I do not come, and I will even go.” That awful sentence-“He that believeth not shall be damned,” was added not out of anger, but because the Lord knew our silly madness, and that we should refuse our own mercies unless He thundered at us to make us come to the feast, “Compel them to come in”; this was the Word of the Master of old, and that text is part of the carrying out of that exhortation, “Compel them to come in.” Sinner, you cannot be lost by trusting Christ, but you will be lost if you do not trust Him, ay, and lost for not trusting Him. I put it boldly now-sinner, not only may you come, but oh! I pray you, do not defy the wrath of God by refusing to come. The gate of mercy stands wide open; why will you not come? Why will you not? Why so proud? Why will you still refuse His voice and perish in your sins? ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/0361.cfm