The answer
Rahab and Ruth became part of the Jewish people and adopted all their customs and traditions. On the other hand, the Gentiles that were converting to Christianity were abandoning the Mosaic Law. Thus, the Jews wanted them to first follow the Mosaic Law and then add the Christian doctrine.What is mentioned in Acts 10 is that Cornelius was praying and giving alms. Nothing was mentioned about him following Jewish customs, or the Jewish Law as far as rules according Leviticus or the Mosaic Law, or if the prayers were in accordance to Jewish rites, or if he was following the Ten Commandments. It was the hard-core Judaizers that disputed with St. Peter about eating with Cornelius, who was a Gentile. However the Jewish Christians that heard St. Peter's explanation and interpretation of the dream (Acts 11) glorified God and believed that God could accept now the Gentiles and they, too, could have an inheritance in the kingdom of heaven.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)