Why are two or three witnesses needed in Deuteronomy 17:6 and 19:15?

But notice first that the idea of difference, and to a large extent the assumption of evil as present, enters into the better significance itself. "The testimony of two men is true," says Scripture. But how is it "true"? May not the testimony of one be true too? Undoubtedly, the meaning is, it can be taken as true; it is valid as evidence. But why cannot the testimony of one be taken as true? Well; the witness may be mistaken, of course: even that will be probably due to defect in some way, — to evil, in this sense of evil; but how often, even so, may real mistake be due to something worse than this! how frequently is it due to prejudice, passion, enmity, and such like! And the moral reason is, in fact, the principal one, why a single witness is to be distrusted so much, if not refused: evil has come in; and there is the main need of a second witness to confirm the first.

But in any case the truth or validity of the double witness is founded upon difference. If upon examination we find the second witness only repeating the testimony, — still more, the words of the first, this correspondence, instead of producing greater confidence, destroys it. We say, this is a contrived affair: the one has learned his lesson from the other. We need the evidence of two persons, not of one; and this is only one person talking with two mouths. We need to have diversity of interests, feelings, general standard, with yet a confirmation of the point in question, — a sort of stereoscopic view of the facts, which shall give them due solidity. Thus the very help given in seconding implies a difference, often a moral one: in other words, the presence of evil.

Hence the difficulty which divines have found, in what they supposed the going back to matters of religion, is in point of fact a mere mistake of their own from divorcing that which God has joined together. We have had fully the direct instruction as to what concerned His own glory, but now even when He is touching on that which bears on man's life, He interweaves religious elements not at all as a repetition of the past, but as connecting it with the present subject. Further, we find that the subject is pursued to show the place of testimony. By the mouth of two witnesses or three it was ordained that he who was worthy of death should die. This was of great value in practice, and is made use of largely in the New Testament — a principle which no man can ever neglect without loss.

At first sight it may seem singular that the Spirit of God should attach so much importance to the requirement of two or three witnesses; but let us remember that we are here learning the ways of God actively dealing with a people on earth, after He had brought them into relationship with Himself. Undoubtedly, if God took no active concern in man or his ways, there might be difficulties. Israel alone, of all the nations on the face of the earth, stood on such a ground as this; and on them God laid the necessity of demanding such testimony. But He is always wise, and besides He would teach His people to trust that He will always give whatever is necessary according to His' own order.

Confirmation in the way of testimony: "The testimony of two men is true." And we have seen that the power of this confirmation depends much on the diversity of the witnesses (2 being the expression of difference).

One often hears, for the purpose of illustrating the Revelation, a reference to Isaiah, Jeremiah, or the like; but we should bear in mind that these prophecies are not in their structure symbolical. Therefore the reasoning founded on the books and style of Jeremiah or Isaiah (Ezekiel being partly symbolical, partly figurative) cannot decide for Daniel or the Apocalypse. Here the figures have a language of their own. Thus the regular meaning of "two," if figuratively used, is competent testimony — enough and not more than enough. "In the mouth of two or three witnesses shall every word be established." According to Jewish law a case could not be decided by one witness; there must be at least two for valid proof and judgment.

However, the testimony of one witness would not be sufficient to pass a death sentence: there must be two or three witnesses (v.6). Also the witness would be required to be first in putting the offender to death (v.7). This would make people slow to witness if they were not persuaded fully of the guilt of the accused.

Two or three witnesses are necessary as regards making a decision in any matter. One witness may be mistaken or prejudiced, or even dishonest. If two people have a controversy, they must stand before the judges and have the matter thoroughly investigated. If one testified falsely, he must suffer the judgment he desired against his opponent (vs.18-19). Under law there was no mercy -- eye for eye, tooth for tooth.

That there should be a sufficient number of witnesses to put the matter of fact beyond the possibility of collusion or fraud.

The mere number of witnesses does not decide, but their age must be considered, and also whether they are independent witnesses, or merely copies of one another.

The next step to be taken; if the first be ineffectual, is to "take with thee one or two more, that in the mouth of two or three witnesses every word may be established." These witnesses are not to establish the truth of the charge: for of this the one who has sinned is already "convicted," but to bring the influence of the truth to bear upon him the more by their confirmation. They are a jury of appeal to make him realize the gravity rather than the truth of his sin; ― a midway step between the private reasoning and the full publicity of the assembly. Love would yet spare the person, while it cannot spare the sin and therefore the present procedure.

We have already had occasion to refer to the great principle laid down in the foregoing passage. It is one of immense importance, namely, the absolute necessity of having competent testimony ere forming a judgement in any case. It meets us constantly in scripture, indeed it is the invariable rule, in the divine government, and therefore it claims our attention. We may be sure it is a safe and wholesome rule, the neglect of which must always lead us astray. We should never allow ourselves to form, much less to express and act upon a judgement without the testimony of two or three witnesses. However trustworthy and morally reliable any one witness may be, it is not a sufficient basis for a conclusion. We may feel convinced in our minds that the thing is true because affirmed by one in whom we have confidence; but God is wiser than we. It may be that the one witness is thoroughly upright and truthful, that he would not, for worlds, tell an untruth or bear false witness against any one; all this may be true, but we must adhere to the divine rule, "In the mouth of two or three witnesses shall every word be established."