The reading is from St. Paul's First Letter to the Corinthians 10:5-12

Brethren, God was not pleased with most of the fathers; for they were overthrown in the wilderness. Now these things are warnings for us, not to desire evil as they did. Do not be idolators as some of them were; as it is written, "The people sat down to eat and drink and rose up to dance." We must not indulge in immorality as some of them did, and twenty-three thousand fell in a single day. We must not put Christ to the test, as some of them did and were destroyed by the Destroyer. Now these things happened to them as a warning, but they were written down for our instruction, upon whom the end of the ages has come. Therefore let any one who thinks that he stands take heed lest he fall.