The statement that a Christian can know that he has eternal life is that already quoted: “These things have I written unto you that believe on the name of the Son of God, that ye may know that ye have eternal life” (5:13). But to this many similar statements found throughout the letter may be added: “by this know we that we are in him” (2:5); “I write unto you, little children, because ye have known the Father” (2:13); “ye have an unction from the Holy One, and ye know all things” (2:20); “I have not written unto you because ye know not the truth, but because ye know it” (2:21); “Beloved, now are we the children of God” (3:2); “we know that we have passed from death unto life” (3:14); “we are of the truth” (3:19); “we know that he abideth in us” (3:24); “ye are of God, little children” (4:4); “by this know we that we dwell in him, and he in us” (4:13); “we know that we love the children of God” (5:2); “we know… we know… we know” (5:18-20).
If these are true statements and if they apply to Christians living at all periods of history, as John obviously implies, then they are of great importance today. For there has hardly been an age in which confusion and uncertainty have been more dominant. Today’s world puts a high premium on knowledge and on the confidence it is supposed to bring. But knowledge has outstripped the ability of most persons to absorb it, except in one or more highly specialized areas; and even in the area of a person’s specialty change comes so rapidly that what was apparently true during the years of the student’s preparation is often outmoded before he enters middle age. Can a person really know anything for certain in such circumstances? Are there any absolutes? Is there anything that will be true, not only today, but tomorrow and the day after that as well? John replies that in spiritual matters, which are the most important anyway, there can be certainty. And if this is true, then this is obviously a message that our age (as well as every age) needs to hear.
It is obvious that such a statement can easily lead to presumption, however. That is, a person can claim a certainty which is in fact unfounded. Or, to put it in John’s words, he can claim to be a child of God when actually he is not, or, which is worse, when he is a child of the devil. How can a person who claims to be a believer guard against such presumption?
In answer to this problem John offers three tests which in one form or another are repeated again and again throughout the letter. They are: the moral test (the test of righteousness or obedience), the social test (the test of love), and the doctrinal test (the test of belief in Jesus Christ).
The first is the test of practical righteousness in the believer’s life. It does not mean that the Christian must be without sin—indeed, John says that the one professing to be without sin deceives himself and makes God a liar (1:8, 10)—but it does mean that he must be progressing in righteousness so that his profession is increasingly matched by his conduct. Any claim to a higher experience of Christianity that is not matched by superior moral conduct is to be rejected (1:6). The second test is the test of the Christian’s relationship to other Christians. Does he love the brethren? Since God is love and since love comes from Him, anyone claiming to know God but failing to show love for others is either self-deceived or is attempting to deceive. The third test is theological, for it is John’s claim that no one who fails to believe that the pre-existent Son of God, the second person of the Trinity, became flesh at a fixed point in time and history and died for our sin can be a Christian. On the one hand, these tests challenge presumption. They are tests by which everyone who claims to be a Christian may examine himself to determine whether he is actually a child of God or not.
On the other hand, they can also (and should also) lead a Christian into that holy boldness in his approach to God which is his privilege and right as a Christian and can endow his speech with that note of authority which he needs as he attempts to bear witness to other persons.
