Cornelius was frightened and wanted to know why God's messenger had come. Barnes says he was afraid "at the suddenness and unexpected character of the vision," and calls the question "the expression of surprise and alarm." Gill points to the brightness and majesty in which the angel appeared, and takes the question to mean, "What is the matter? what is to be said or done?" Matthew Henry hears two things in it: Cornelius speaks "as one afraid of something amiss," yet also as "one desirous to know the mind of God, and ready to comply with it."

The angel answered, "Thy prayers and thine alms are come up for a memorial before God" (Acts 10:4). Then he told Cornelius to send men to Joppa for "Simon, whose surname is Peter," who "shall tell thee what thou oughtest to do" (Acts 10:5-6). Matthew Henry says, "Without dispute or delay Cornelius was obedient to the heavenly vision." When the angel had departed, he called two household servants and a devout soldier and sent them to Joppa (Acts 10:7-8).

A centurion was a Roman army officer, so Cornelius was a Gentile, not a Jew. Yet he "feared God with all his house" and "prayed to God alway" (Acts 10:2). He later told Peter that he was praying in his house at the ninth hour when the angel came (Acts 10:30).

"Memorial" means something kept in remembrance before God. Barnes explains it simply: they "are remembered before God." Gill compares them to sacrifices on the altar, which "ascended to God with acceptance."

This question opens one of the great turning points in Acts. God had been hearing the prayers of a Gentile soldier, and He sent an angel to tell him so. Matthew Henry notes that his prayers and alms were accepted through Christ. Peter later drew the lesson himself: "God is no respecter of persons: but in every nation he that feareth him, and worketh righteousness, is accepted with him" (Acts 10:34-35).

Yet the angel did not preach the gospel to Cornelius. He sent him to Peter, who would tell him "words, whereby thou and all thy house shall be saved" (Acts 11:14). God honored Cornelius' seeking by bringing him the message of Jesus through a human messenger.