Bill DeJong writes:
Paul’s argument in 1 Corinthians 10 is that Christian baptism does not guarantee our eternal security regardless of how we live. For proof, Paul appeals to the baptism of the Israelites. They were baptized folk just as we are baptized folk. They had the covenant promise just as we have the covenant promise. But covenant promises must be “mixed with faith” (Hebrews 4). Because the Israelites were unbelieving and disobedient their bodies are scattered in the wilderness. Therefore we baptized folk must be believing and obedient unlike the wilderness Israelites. If we stand, we must take heed, lest we fall.
This passage makes sense only if we grant substantial continuity between old and new covenants.