What exactly does Moses mean when, in 1 Corinthians, he mentions that the Israelites were “batpized into Moses”?
From Haydock’s Catholic Bible Commentary:
In Moses. Under the conduct of Moses they received baptism in figure, by passing under the cloud and through the sea: and they partook of the body and blood of Christ in figure, by eating of the manna, (called here a spiritual food, because it was a figure of the true bread which comes down from heaven) and drinking the water miraculously brought out of the rock, called here a spiritual rock; because it was also a figure of Christ. (Challoner) — Were baptized in the cloud, and in the sea, figuratively, these being figures of baptism in the new law. As Moses, who delivered them from the slavery of Egypt, was a figure of Christ, who came to deliver mankind from the slavery of sin. (Witham)
Paul is pointing out that the realities of Christian life – in particular, the sacraments – were prefigured by the experience of the Israelites; they participated in a ‘baptism’, passing through the Red Sea, and were fed spiritual food and drink. Yet, this prefigurement wasn’t ‘magic’ – it didn’t automatically save them – they fell from grace and were lost.
Paul is warning Christians, then, that they shouldn’t be overconfident: just because they were baptized, and just because they share in the Eucharist, doesn’t mean that they themselves are immune – they, too, are capable of falling from God’s grace, just as the Israelites did in the past!