For what if some did not believe? – Romans 3:3

…he that believeth not is condemned already… – John 3:18

The question of the apostle is, “What if some did not believe?” Well, if I had to ask and answer that question, at this time, I would say, “What if some do not believe?” Then they are lost. “He that believeth not is condemned already, because he hath not believed in the name of the only-begotten Son of God.” There still remains, to those who hear the gospel, the opportunity to believe; and, believing in the name of the only-begotten Son of God. There still remains, to those who hear the gospel, the opportunity to believe; and, believing, they shall find life through the sacred Name. Let us pray for them. If some do not believe, let us, who do believe, make them the constant subject of our prayers; and then let us tell them what it is to be believed, and bear our witness to the saving power of the gospel. When we have done that, let us scrupulously take care that our life and conduct are consistent with the doctrine that we teach, so that, if some do not believe, they may be won to Christ by the example of those who believe in Him. Oh, that every Christian here would seek to bring another person to Christ! I pray you, beloved, if you have tasted that the Lord is gracious, be not barren nor unfruitful. If you know the great secret, tell it to others. Tell it out; tell it out; we all want stirring up to this blessed work; I am sure we do. I heard of a Christian who always spoke about Christ to at least one person every day. I commend the example for your imitation. How many of us could say that we do that? I know there are some here who do ten times as much as that. It has grown to be a habit with them to speak of Christ to every one they meet; but it is not the habit even of all who believe. It takes some Christians a long time to begin to say anything for their Lord. Let us try and labour hard, that, if some people do not believe, we may bring them to the Saviour, that God may have praise from them also. ~ C.H. Spurgeon

https://www.blueletterbible.org/comm/spurgeon_charles/sermons/2255.cfm