Such being the power of Christ's work in its twofold aspect of propitiation and of intercession, the same practical issues as in the preceding section were shown to flow from the revealed nature of God are here, in somewhat different form, linked with that work. First, keeping his commandments (which is equivalent to 'walking in the light') is the test to ourselves, as well as to others, of our really knowing Him with a knowledge which is not mere head work, but the acquaintance of sympathy and friendship, or, in the words of the previous paragraph, having fellowship with Him.
Clearly, the scope of this section requires that 'His commandments' should here mean Christ's, not the Father's. All professions of knowing Jesus which are not verified by obedience to Him are false. If we do keep His word--not merely the individual 'commandments,' but the word as one great whole--our love to God reaches its perfection, for it is no mere emotion of the heart, but the force which is to mould and actuate all our acts.
Verse 5 _b_ should be separated from the preceding words, for it is really the beginning of the second issue from the work of Christ, and is parallel with 'hereby know we,' etc., in verse 3. Observe the progress in thought from the assurance that we _know_ (ver. 3) to the assurance that we _are in_ Him. The Christian's relation to Jesus is not only that of acquaintance, however intimate, loving, and transforming, but that of actual dwelling in Him. That great truth shines on every page of the New Testament, and is not to be weakened down into metaphor or rhetoric. It is the very heart of the Christian life, and the test that we have attained to it, and that not merely as an occasional, but as a permanent, condition (note that '_are_ in Him' is strengthened to '_abideth_ in Him') is that our outward life, in its manifold activities, shall be conformed to the pattern of all holiness in the life of Jesus. To walk as He walked is to walk in the light. Profession is nothing, conduct is everything, and we shall only be clear of sin in the measure in which we have Him who is the light of men for the very life of our lives.