Gurthrie provides a fourth and fifth reason that an interest in Christ may not be known:
Fourth: They don’t actually know what evidence would satisfy them. Some people seem unwilling to receive God’s promise upon God’s Word. Such people want an additional help – but they are not sure what that would be. These people wish to set up their own standard for assurance, when God has given us his own standard and good grounds (1 John 1:4, 5:10 & 13).
By demanding a standard of proof that God has not promised, there can be no other than disappointment.
Fifth: Expecting some experience to be sufficient evidence. Guthrie calls this “changeable evidence.” He provides three examples:
(1) I never sin. Yet where in Scripture do we find a promise that we will never sin? While there is no excuse for sin, the Scripture assumes that we will and that God will forgive (see, e.g., 1 John 2:1).
(2) I always have a sensible answer to my prayer. Again, where does God promise that an angel will always come down and tell me how God intends to respond to a particular prayer.
(3) I will always have a sensible witness of the Spirit – I will always feel saved.
In each of these instances, the believer claims that an experience will suffice to provide a basis of assurance. Yet, experience is changeable: it is never as strong as the last few moments of experience. Thus, Peter tells us to place our confidence on something more solid than experience: “something more sure [than even the greatest of experiences], the prophetic word” (2 Pet. 1:19).
In short, when one seeks for assurance in something other than the manner prescribed by God, one should not be surprised that assurance is not forthcoming. Therefore, assurance made be hand – but only along the lines prescribed in the Bible.