How Do We Know?

How do we know if someone is speaking the truth about Jesus?

“By this you know the Spirit of God :Every spirit that confesses that Jesus Christ has come in the flesh is of God, and every spirit that does not confess that Jesus Christ has come in the flesh is not of God. And this is the spirit of Antichrist, which you have heard was coming, and is now already in the world.”                    I John 4:2,3  NKJV

“Who is a liar but he who denies that Jesus is the Christ? He is antichrist who denies the Father and the Son. Whoever denies the Son does not have the Father either; he who acknowledges the Son has the Father also.”                         I John 2:22,23  NKJV