Context: Continuing on the prohibition of pagan feasts, Paul warns the Corinthians against their false security because their participation in the sacraments (baptism and the Lord's Supper) does not guarentee their salvation. This point is illustrated by the example of Israel in their exodus from Egypt.
"our forefathers": the Corinthian Gentiles are clearly not the descendants of the Israelites; the term is used to express the truth that God's new people (the Christian church) are the true Israel of God. Some theologians believe that the universal Church began in Abraham.
"baptized into Moses": may mean unity of the Israelites under Moses's leadership; not found in OT but in the Christian language of believers baptized into Christ (Gal 3:27, Ro 6:3).
"The cloud" was the means by which the Lord "went before them" to lead them (Ex 13:21).
The crossing of the Red Sea is used as a model (or type) for Christian baptism. Just like the Isrealites, Christians are guided by God ("in the cloud") and receive baptism.
The eating of manna and the drinking of water from the rock are used as a model for the wine and bread in the Lord's Supper. They are "spiritual" in the sense of provision from God.
"Spiritual rock" is a reference to the popular rabbinic interpretation of Nu 21:16-18 that the well (known as Miriam's well, a rock with the size of a large round vessel) they brought with them in the desert provide continuous and miraculous source of water. Paul identifies the rock with Christ to emphasize that it was by Christ himself that they were being nourished in the wilderness.
Despite these sacred privileges similar in kind to the Corinthians, including the presence of Christ himself to nourish them with "spiritual drink", the Israelites experienced God's judgment and failed to obtain the prize.
4 examples of how "privileged" Israel "lusted after evil things". The examples were chosen because in a very precise way they reflect the situation in Corinth.
Eating pagan meals in the idol temples is idolatry (v.14). This example points to pagan feasts in particular, not to idolatry in general, because otherwise the first half of Ex 32:6 should be quoted: "the people rose early and sacrificed burnt offerings and presented fellowship offerings". Instead, the second half of the verse is quoted here.
The example refers to Nu 25:1-9. Here, eating in the presence of the idol and sexual play are specifically connected. Further, every mention of "idol food" in the New Testament is accompanied by a reference to sexual immorality (Ac 15:29; Rev 2:14, 20).
The example refers to Nu 21:4-7 where Israel complained and "spoke against God and against Moses". In 10:21-22 Paul makes it clear that the Corinthians' challenge of Paul's prohibition against pagan feasts is a testing the Lord. Paul asked in the language of Dt 32:16 "Are we trying to arouse the Lord's jealousy?"
The example refers to Nu 14:1-38 where Israel grumbled against Moses as their leader. The result was a plague which is associated here with "the destroying angels". In this example also is the pronouncement that only Joshua, Caleb, and those under 20 would enter the promised land. This example is used to reflect their grumbling against Paul.
The one who thinks he is standing firm and who think their participation in the Christian sacraments has placed them above danger (in regard to pagan feasts) might fall, just as the Israelites, and fail to get the prize (refused entry to the promised land, loss of salvation).
There is no risk of falling as long as one is dealing with ordinary trials. Moreover, they can expect divine aid. But with deliberate acts of "testing" Christ (v.9) there is no divine aid; they must therefore flee from idolatry (v.14).
For the Corinthians, the temptation is the pressure of eating pagan feasts with pagan friends. A person under trial or temptation does not need to succumb because God is faithful; he can be counted on to help them: