Thomas, not yet having seen Christ after His resurrection, doubted the resurrection's reality. But upon encountering the risen Christ, Thomas exclaimed, "My Lord and My God!" Christ's reply to Thomas' statement is very telling.
The second appearance of the verb "seen" here is the same Greek word that is often translated as "know," as it is in verse 14. Mary is outside the sepulcher, and she saw Jesus and did not know that it was He. It could just as easily read that she "did not see that it was Jesus." In English, we often connect the idea of sight with knowledge or with knowing. We do it all the time. We can be staring at a formula or a concept straight in the face, as it were, and not understanding it or not agreeing, and we simply say, "I don't see it." And when the light finally dawns, we say, "Oh, yes! Now I see it. Now I understand."
Yet Jesus says, "Blessed are those who have not seen"—those who lack full understanding and knowledge—"and yet have believed." "Believe" here is the verb form of the Greek noun that is often translated as "the faith." Christ promises the blessing to those who do not see, who do not have full understanding, but who nevertheless believe. We often expect to know and understand so much, yet we are to live by faith.
Believing the prophetic word and putting into practice the commands to repent, to keep, and to watch that appear so often in God's prophetic word are walking by faith rather than by sight or by knowledge. Paul mentions this in II Corinthians 5:7.
To Watch and Keep
Other Forerunner Commentary entries containing John 20:28:
1 John 5:1-8