“Whoever confesses that Jesus is the Son of God, God abides in him, and he in God.” (I John 4:15)
Despite the apparent simplicity of this verse, one should be careful not to take it in a woodenly literal fashion, as a minimalist means of salvation: just confess that Jesus is the Son of God, with no commitment of your life to Him, and you will be saved. For “Exhibit A’, we need only look as far as Mark 5:7:
In the story of the Gerasene Demoniac there, when the demons were summoned to Jesus, they came up and addressed Him as “Jesus, Son of the Most High God.” These demons confessed that Jesus was the Son of God. And yet no one would consider making a case for their salvation based upon this “confession”!
So there is something more involved here than merely making a mere confession with one’s lips of who Jesus is. Rather “confess” should be taken more broadly: meaning to agree with the entirety of who Jesus is, and what He came to do — for YOU, because of YOUR sin, and because of that, to commit your life to Him because He is indeed the Son of God and worthy of your love and obedience. Thus to “confess” Jesus here means to agree with all that He is and represents, and committing your life to Him accordingly.
Now, must a person understand the absolute entirely of Jesus’ life and work in order to be saved? No; none of us would be saved in that eventuality. But the subsequent life of a person who has confessed Jesus will demonstrate whether they have really committed themselves to Him — and that is to a great extent what this Book of I John is all about: it contains several tests and proofs that confirm whether you are really His: walking in the light, purifying your life from sin, loving Christian brothers, confessing Christ publicly, etc.
But the key here is to understand is that a mere “confession” alone must not be taken as a cheap substitute for a genuine commitment of one’s life to Christ. Remember, in Matthew 7:21 Jesus warned: “Not everyone who says to Me, ‘Lord, Lord’ will enter the Kingdom of Heaven, but he who DOES the will of My Father who is in heaven.”