Acts 26:3

To be expert - To be skilled or well acquainted.

In all customs - Rites, institutions, laws, etc. Everything pertaining to the Mosaic ritual, etc.

And questions - Subjects of debate, and of various opinions. The inquiries which had existed between the Pharisees, Sadducees, scribes, etc. Paul could say this of Agrippa without falsehood or flattery. Agrippa was a Jew; he had passed much of his time in the kingdom over which he presided; and though he had spent the early part of his life chiefly at Rome, yet it was natural that he should make himself acquainted with the religion of his fathers. Paul did not know how to flatter people, but he was not unwilling to state the truth, and to commend people as far as truth would permit.

Wherefore - On this account; because you are acquainted with those customs. The Romans, who regarded those customs as superstitious, and those questions as matters to be treated with contempt, could not listen to their discussion with patience. Agrippa, who knew their real importance, would be disposed to lend to all inquiries respecting them a patient attention.