Albert Barnes Commentary Acts 17:9

"And when they had taken security from Jason and the rest, they let them go." — Acts 17:9 (ASV)

And when they had taken security of Jason. This is an expression taken from courts, meaning that Jason and the other satisfied the magistrates concerning the good conduct of Paul and Silas, and became responsible for it. Whether this was done by depositing a sum of money, and thus giving bail, is not quite clear. The meaning is that they acted in accordance with Roman customs and gave sufficient security for the good conduct of Paul and Silas.

Heuman supposes that the pledge given was that they would leave the city. Michaelis thinks that they gave a pledge that they would no longer harbor them; but that if Paul and Silas returned again to them, they would deliver them to the magistrates.

And of the other. This refers to the other brothers (Acts 17:6) who had been drawn before the rulers of the city.