Clearly, Paul knew the story better than you do. The warning was for sinners, those in unbelief.
The spiritual food was manna and the spiritual drink was water from the rock. The poison of the serpents referred to the serpent on a pole and those killed were in unbelief. Those who sinned were unbelievers. They entered not in because lack of faith....unbelief. That is the point Paul is making here.
It's spoken of in Hebrews, as well. Actually, if you had read the OT, you'd know this.
The warning was not entering in because of UNBELIEF.
Heb. 4:1-6KJV Let us therefore fear, lest, a promise being left us of entering into his rest, any of you should seem to come short of it. For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it. For we which have believed do enter into rest, as he said, As I have sworn in my wrath, if they shall enter into my rest: although the works were finished from the foundation of the world. For he spake in a certain place of the seventh day on this wise, And God did rest the seventh day from all his works. And in this place again, If they shall enter into my rest. Seeing therefore it remaineth that some must enter therein, and they to whom it was first preached entered not in because of unbelief:
Heb. 4-10-11 For he that is entered into his rest, he also hath ceased from his own works, as God did from his. Let us labour therefore to enter into that rest, lest any man fall after the same example of unbelief.
