Paul is referring to the time of Moses in the book of Exodus when Israel fled through the Red Sea as the Egyptian army pursued them. Here "our" refers to Paul and includes the Corinthians. The Corinthians were not acutal descendants of the Israelites who escaped Egypt. Paul means that all Christians are spiritual descendants of Israel. Alternate translation: "our ancestors" (See: [[rc://en/ta/man/translate/figs-exclusive]])
When the Israelites left Egypt, God traveled with them in a pillar of cloud. Alternate translation: "were all led by God who was in the cloud" (See: [[rc://en/ta/man/translate/figs-explicit]])