Albert Barnes Commentary Acts 28:20

"For this cause therefore did I entreat you to see and to speak with [me]: for because of the hope of Israel I am bound with this chain." — Acts 28:20 (ASV)

Because that for the hope of Israel. On account of the hope which the Jews cherished of the coming of the Messiah; of the resurrection; and of the future state through him. (See Barnes on Acts 23:6).

I am bound with this chain. (See Barnes on Acts 26:29).

Probably he was attached constantly to a soldier by a chain.