to get a person to commit himself as to his opinion.
You couldn't imagine the time that Ahab tried to pin Elijah down. Could you imagine the time that the Pharisees tried to pin Jesus down?
to secure or fasten firmly.
Now, I don't want to hurt you, but I got to pin this down so this church will know what... We're not here as a bunch of illiterate crack pots; we know where we are standing in the Word of God.