This verse is a supplement to the previous verse, and speaks of the other articles of the pledge taken by the Israelites. They had agreed not to kill one another by engaging themselves in an internecine war, and also not to send their men into exile - that is to say, not to harass a man so as to force him to migrate.
They had willingly taken this pledge. Now, it may sometimes happen that one does not express one's willingness in so many words, but the manner of his speech suggests it. The agreement of the Israelites was not of this order, but as clear and explicit as the statement of a witness usually is.