Joshua 24:22

And Joshua said unto the people
In reply to their answer and resolution:

ye [are] witnesses against yourselves, that ye have chosen you the
Lord God to serve him;
that is, should they, after this choice of him, which they had so publicly declared, desert his service, and go into idolatry, their testimony would rise up against them, and they would, be self-condemned:

and they said, [we are] witnesses;
should we ever apostatize from the Lord and his worship, we are content to have this our witness produced against us.