But even if we suppose that he does mean this we have still to explain the _practice_ of those who were well aware of Christ's command respecting swearing, and certainly had no intention of deliberately violating it. If the first Christians were willing on certain occasions to take certain oaths, it must have been because they were fully persuaded that Jesus Christ had not forbidden them to do so. When called upon by heathen magistrates to take an oath, the distinction which they drew was not between swearing and not swearing, but between taking oaths that committed them to idolatry and oaths which did nothing of the kind. The latter oaths they were willing to take. Thus Tertullian says that they would not swear by the _genii_ of the emperors, because these were supposed to be demons; but by the safety of the emperors they were willing to swear (_Apol._ xxxii.). Origen writes to much the same effect (_Con. Celsum_, viii., lxv.). The oath by the _genius_, or _numen_, or "fortune" (τύχη) of the emperor was recognized as a formula for abjuring Christianity. Thus the proconsul presses Polycarp again and again: "Swear by the genius of Cæsar; swear the oath, and I will release thee" (_Mart. Pol._ ix., x.); and the fear of being betrayed into an act of idolatry was one of the main reasons why the early Christians disliked taking oaths. But there was also the feeling that for Christians oaths ought to be quite unnecessary. Thus Clement of Alexandria says that the true Christian ought to maintain a life calculated to inspire such confidence in those without that an oath would not even be demanded of him. And of course, when he swears, he swears truly; but he is not apt to swear, and rarely has recourse to an oath. And his speaking the truth on oath arises from his harmony with the truth (_Strom._ vii., viii.). Pelagius maintained that all swearing was forbidden; but Augustine contends, on the authority of Scripture, that oaths are not unlawful, although he would have them avoided as much as possible (_Ep._ clvii. Comp. _Epp._ cxxv., cxxvi.).
But there is not only the evidence as to how the primitive Church understood the words of Christ and of St. James; there is also the practice of St. Paul, who frequently calls God to witness that he is speaking the truth (2 Cor. i. 23; xi. 31; xii. 19; Gal. i. 20; Phil. i. 8), or uses other strong asseverations which are certainly more than plain Yea and Nay (Rom. ix. i.; 1 Cor. xv. 31; 2 Cor. i. 18; xi. 10). Augustine quotes St. Paul in defence of swearing, but adds that St. Paul's swearing, when there was weighty reason for it, is no proof that we may swear whenever we think proper to do so. And in the Epistle to the Hebrews the fact that men swear in order to settle disputes is mentioned without any intimation that the practice is utterly wrong. On the contrary, we are told that God has condescended to do the same, in order to give us all the assurance in His power (vi. 16-18).
Lastly, we have the convincing fact that Jesus Christ allowed Himself to be put upon His oath. After having kept silence for a long time, He was _adjured_ by the High Priest to answer; and then He answered at once. The full meaning of the High Priest's words are, "I exact an oath of Thee (ἐξορκίζω σε) by the Living God" (Matt. xxvi. 63, 64). Had this been an unlawful thing for the High Priest to do, our Lord would have kept silence all the more, or would have answered under protest.
II. It remains to consider the relation of the prohibition of swearing in this Epistle to the almost identical prohibition in the Sermon on the Mount. Is St. James quoting Christ's words? and if so, whence did he derive his knowledge of them?