The peace and harmony of the church are disrupted by such who “crept in unawares” (Jude 3) into the congregation of God’s people. There the beloved Apostle’s counsel is that they are to “mark them” these. The word means “to spy out, look towards an object, to contemplate, give attention to”. God’s people are to be on the look out for such trouble-makers that can destabilise the faith of God’s people.