There are various classes of Sceptics and the same methods of dealing will not answer for all.
1. _Skeptics who are mere triflers._ With such use 1 Cor. i. 18. If a man says the Bible is foolishness to him, you can say “Yes, that is just what the Bible itself says.” He will probably be surprised at this reply and then you can show him 1 Cor. i. 18; “the preaching of the cross is to them that perish foolishness.” Then you can say to him, “You see that the Bible says that it is foolishness to some—them that _perish_—and the reason it is foolishness to you is because you are perishing.” 1 Cor. ii. 14, can be used in a similar way. A worker was one night dealing with a man who said to him when he was trying to persuade him to come to Christ, “all that you are saying is foolishness to me.” The worker quickly replied, “Yes, that is just what the Bible says.” The man looked at him in astonishment and said: “What?” “You said all that I have been saying to you was foolishness to you, and that is just what the Bible says.” The man was more astonished then than ever and the worker turned him to 1 Cor. ii. 14, “But the natural man receiveth not the things of the Spirit of God; for they are foolishness unto him; neither can he know them because they are spiritually discerned.” The man said “I never saw that before; I never thought of it in that light before.” 2 Cor. iv. 3, 4, is very useful in showing the trifler that he is lost and that his skepticism arises from the fact that the “god of this world hath blinded his mind.” 2 Thes. ii. 10‒12, is useful in showing the origin of skepticism, “because they received not the love of the truth” and the consequences of skepticism—delusion and damnation. John viii. 21, 24, is also very searching in dealing with this class of skeptics, showing the terrible consequences of unbelief. John v. 44; iii. 18, 19, 20 expose the origin of scepticism. Ps. xiv. 1, is useful in some cases though one needs to be guarded in its use, using it only when it can be done with earnestness and tenderness. 2 Thes. i. 7, 8 can also be used with good results.
2. _Serious minded skeptics._ There is a large class of men and women in our day who are really desirous of knowing the truth but who are in an utter fog of skepticism. John vii. 17 is a very helpful passage in dealing with such. It shows the way out of skepticism to faith. Get the skeptic to act along the line of that verse. Put to him the question, “Will you surrender your will to God and promise to search honestly and earnestly to find out what God’s will is that you may do it, to ask God to show you whether you need a Saviour and whether Jesus is a Divine Saviour, the Son of God; and will you promise that, if God will show you that Jesus is the Son of God, to accept Him as your Saviour and confess Him before the world?” Have him make his promise definite, by putting it down in black and white. If you get him to do this, his skepticism will soon take wings.