=== While our lives as Christians are characterized in general with an attitude of faith and assurance, that is not to say that there will never be times when unbelief, like any other sin, clouds our judgment ( c.f. Mark 9:23-25..."I do believe; help me in my unbelief!") ===

My response: It's crucial to look at WHEN the centurion said "help my unbelief". This was BEFORE the Resurrection. And before the Resurrection, NOBODY -- including John the Baptist and Thomas -- could be certain that Jesus was the Christ. They all had doubts and uncertainties about his messiahship. Nobody could be certain that Jesus was the Christ until the Resurrection. Why? Because Christ said the Resurrection was the ONE SIGN He would give to prove His Sonship. So the only way the centurions unbelief could be cured was by the Resurrection, which would have proved to Him that Jesus was the Christ. Indeed as Peter says in Acts, the Resurrection was God's declaration to all men that Jesus is the Christ.

Therefore, BEFORE the Resurrection NOBODY could be sure that Jesus was the Christ. However, after the Resurrection and Pentecost, the Holy Spirit declared Jesus to be the Christ. Therefore, anyone today who denies Jesus' Messiahship is blaspheming the Holy Spirit. Unless they repent (have a change of mind) they will likewise perish.


What about doubting Thomas? Of course, yes, Thomas was a saved man when he doubted the Resurrection of Christ. But he was a saved JEW. He was living BEFORE Pentecost. And before Pentecost NOBODY understood the Resurrection! This is why Christ said to Peter, "When you are CONVERTED, comfort the brethren." And to his disciples he said, "I WILL SEND you the Comforter".

Of course, the disciples had the Holy Spirit before Pentecost, but He had NOT yet comforted them about the Resurrection. He only gave them the understanding of this truth at Pentecost.

So, yes, the disciples had doubts about the Resurrection up until Pentecost. But since Pentecost, the fact of the Resurrection has become "THE POWER OF GOD UNTO SALVATION". And the Gospel today is that "Christ was RAISED AGAIN according to the Scriptures." 

Thus  no believer today could have any doubts about the Resurrection, otherwise they would be denying the Apostolic Gospel.

In summary -- 1) The disciples had doubts about the Resurrection until Pentecost when they were given the understanding of it ... so 2) Believers today all understand the Resurrection so they will never doubt it.

And can someone believe THAT JESUS IS RISEN and not know they are a believer? Of course not!