Swearing, Vows, & Oaths

Jesus Christ forbids us from swearing and taking oaths in the well-known Sermon on the Mount. But the Bible also seems to permit and allow swearing in other places; both in the Old and New Testament. God Himself is even listed as one of the Persons who swears. How can we reconcile this area of tension and come to a proper understanding of Jesus' words in the Sermon on the Mount?