The one saying that I know Him but does not guard His commandments is a liar and the truth is not in this one, 1 John 2:4.
If someone claims to know Christ but does not guard His commandments, he is a liar, demonstrating that he does not have experiential knowledge of Christ. The one living by law, or any other commandment, is not living out from faith, for they are not taking God at His word and therefore do not possess an experiential knowledge of Christ.
As the Apostle John continues to write about those who know the resurrected and glorified Christ, he addresses the person who claims to have experiential knowledge of Christ but does not guard His commandments.
The concept of “know” in this passage refers to experiential knowledge, not intuitive knowledge. In 1 John 2:3, John states that the one who guards Christ’s commandments possesses experiential knowledge of Him. These are not the Mosaic commandments, for Christ gave the Church a new commandment: to love one another (John 13:34). John clarifies in 1 John 3:23–24 that these commandments are to believe on the Son, love one another, and abide in Christ.
Although often translated as “keep,” the original word does not merely emphasize action but conveys a sense of protection. His commandments are precious to the one who knows Him; therefore, such a one will guard them to ensure they are being fulfilled in his life. “Keep” focuses on doing for the sake of completing a task, whereas “guard” emphasizes value to the person and therefore a willingness to protect these words by fulfilling them whenever possible.
If someone claims to know Christ but does not obey His commandments, they are a liar. Such a person relies on the Mosaic Law, or a modification thereof, as the standard for conduct instead of grace and the commandments Christ gave to the Church. In doing so, he demonstrates that he lacks experiential knowledge of Christ.