Jn 20:29 – ‘Jesus said to [Thomas], “Have you believed because you have seen me? Blessed are the people who have not seen and yet have believed.”’

2 Cor 5:7 – ‘We live by faith, not by sight.’

Heb 11:1 – ‘Now faith is being sure of what we hope for, being convinced of what we do not see.‘

The danger for preachers (and others) is to appeal to these texts to support the idea that [Christian] faith does not rely on evidence; that it is a leap in the dark.

The first thing to notice is that none of these texts contrast faith with evidence: they all contrast faith with sight.

Now, to take each of them in turn:

John 20:29

John’s Gospel emphasises the value of evidence in a number of ways – eyewitness testimony, resurrection witness, fulfilment of prophecy and miracles as ‘signs’, and so on.  For Thomas, these should have been sufficient; to expect more was to engage in unreasonable doubt.

So the issue is not belief without evidence, but belief without sight.  In recording this, John has in mind on future hearers of the gospel, who will believe without seeing, cf 1 Pet 1:8.

Jesus says to Thomas, in effect, “If you had not seen me alive, you would not have believed.”  He was relying utterly on his own senses.  But, as Matthew Henry observes:

‘If no evidence must be admitted but that of our own senses, and we must believe nothing but what we ourselves are eye-witnesses of, farewell all commerce and conversation. If this must be the only method of proof, how must the world be converted to the faith of Christ?’ (MHC)

John Lennox remarks that

‘some contemporary atheists like A. C. Grayling have used the story of Thomas to buttress their idiosyncratic contention that faith means believing without evidence. He takes Jesus to be saying: “Blessed are those who have had no evidence and yet have believed.” This is an astonishing conclusion for a philosopher, whose stock-in-trade is the analysis of the logic of argument. The point Jesus is making is that not everyone has the evidence of physical sight. But physical sight is not the only kind of admissible evidence. The very next statement in John’s Gospel (how did Grayling fail to see this?) points out what that other evidence is.’  (Against the Flow: The inspiration of Daniel in an age of relativism (pp. 189-190).

2 Corinthians 5:7

This verse is is not about the supposed limitations of knowledge or evidence.  It is, rather, about our relationship with God.  Here and now, in the present life, we experience God partially and mediately; we live by faith.  Then and there, in the life to come, we shall experience God as he is in himself; we shall live by sight.

Hebrews 11:1

Hebrews 11 is not a complete and systematic treatise on faith.  Rather, it explores that aspect of faith by which we trust God for the things we do not [yet] see.  It is using ‘faith’ as a near-synonym for ‘hope’.  And when v3 refers back to creation, it is clear that we have evidence of God’s creative work from the cosmos we see around and above us (see Psa 19 and Rom1), even though we did not see him actually doing that creative work.  More generally, Heb 11 refers both to fulfilled prophecy and to miracles (see v35) as important categories of evidence.  Heb 2 has already referred to the confirming and testifying power of miracles.

See this, by Jason Engwer.