What do Christians know?
According to 1 John 5:18-20, they know three things:
We know that anyone born of God does not continue to sin; the one who was born of God keeps him safe, and the evil one cannot harm him. We know that we are children of God, and that the whole world is under the control of the evil one. We know also that the Son of God has come and has given us understanding, so that we may know him who is true. And we are in him who is true—even in his Son Jesus Christ. He is the true God and eternal life.
The first thing Christians know is the relationship between belief and behavior. Throughout 1 John, John argues that belief in God must result in godly behavior. There is an intimate and necessary connection between faith and works, in other words. In verse 18, John states the matter quite forcefully: “anyone born of God does not continue to sin.” I don’t think that John literally means Christians never sin after the moment of their conversions. Rather, I think he means that sin does not have an abiding power over them. Why? “The one who was born of God keeps him safe.” That is, Jesus protects Christians from any “harm” the “evil one” can do to them. It is Jesus himself who makes possible the ultimate victory of Christians over sin.
The second thing Christians know is the assurance of their salvation. According to verse 19, “We know that we are children of God.” Notice what a strong statement this is! Know. Not think or believe or hope. “Know” is what philosophers call a “success term.” It indicates the successful accomplishment of a desired action. In this case, Christians have succeeded in attaining assurance of salvation. They know they are saved because they have put their trust in Jesus Christ. He is the one who makes knowledge of salvation actual.
And, therefore, it is unsurprising that the third thing Christians know is really a person, Jesus Christ, who makes knowledge of the first two things possible. Verse 20 says, “We know also that the Son of God has come and has given us understanding, so that we may know him who is true,” in other words, God. The reason Jesus Christ entered human history and took on a human nature was to give us the knowledge leading to salvation. He is in the position to give this knowledge because he himself is “the true God and eternal life.”
Obviously, these three pieces of knowledge are tremendously important from a personal and devotional point of view. What a comfort it is to have a personal relationship with Jesus, to receive assurance of salvation, and to be empowered for godly living! And yet, please do not fail to see the theological intensity of John’s personal and devotional remarks. They go straight to the heart, for example, of the doctrines of the Trinity, the Incarnation, and salvation. Doctrine determines spirituality; spirituality reflects doctrine. Truth is practical, and practicality must be truthful. That also is something Christians know.