A. Warnings not to doubt or lose faith:

MAT 14:31. And immediately Jesus stretched forth his hand, and caught him, and said unto him, O thou of little faith, wherefore didst thou doubt?

JOH 20:27. Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing.

LUK 12:29. And seek not ye what ye shall eat, or what ye shall drink, neither be ye of doubtful mind.

LUK 12:30. For all these things do the nations of the world seek after: and your Father knoweth that ye have need of these things.

HEB 3:12. Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God.

HEB 4:11. Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.

HEB 10:35. Cast not away therefore your confidence, which hath great recompence of reward.

B. The consequences of not having faith:

DEU 32:20. And he said, I will hide my face from them, I will see what their end shall be: for they are a very froward generation, children in whom is no faith.

ISA 7:9. And the head of Ephraim is Samaria, and the head of Samaria is Remaliah's son. If ye will not believe, surely ye shall not be established.

MAT 13:58. And he did not many mighty works there because of their unbelief.

JOH 3:36. He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.

ROM 14:23. And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin.

1TIM 1:19. Holding faith, and a good conscience; which some having put away concerning faith have made shipwreck:

HEB 3:18. And to whom sware he that they should not enter into his rest, but to them that believed not?

HEB 3:19. So we see that they could not enter in because of unbelief.

HEB 11:6. But without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him.

JAM 1:6. But let him ask in faith, nothing wavering. For he that wavereth is like a wave of the sea driven with the wind and tossed.

JAM 1:7. For let not that man think that he shall receive any thing of the Lord.

C. Weak or doubting faith seeks miracles & signs:

MAT 16:1. The Pharisees also with the Sadducees came, and tempting desired him that he would shew them a sign from heaven.

MAT 16:4. A wicked and adulterous generation seeketh after a sign; and there shall no sign be given unto it, but the sign of the prophet Jonas. And he left them, and departed.

JOH 20:24. But Thomas, one of the twelve, called Didymus, was not with them when Jesus came.

JOH 20:25. The other disciples therefore said unto him, We have seen the LORD. But he said unto them, Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe.

JOH 20:26. And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you.

JOH 20:27. Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing.

JOH 20:28. And Thomas answered and said unto him, My LORD and my God.

JOH 20:29. Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.

1COR 1:22. For the Jews require a sign, and the Greeks seek after wisdom:

D. Faith or doubt? To do or not to do:

MAT 9:29. Then touched he their eyes, saying, According to your faith be it unto you.

ROM 14:5. One man esteemeth one day above another: another esteemeth every day alike. Let every man be fully persuaded in his own mind.

ROM 14:22. Hast thou faith? have it to thyself before God. Happy is he that condemneth not himself in that thing which he alloweth.

ROM 14:23. And he that doubteth is damned if he eat, because he eateth not of faith: for whatsoever is not of faith is sin.