John 3:16 – For God so loved the world that He gave His only begotten Son, so that whoever believes in Him should not perish but have everlasting life.
Believing in Him is an experience God gives us; it is not something we must do.
If “believing in Him” is something every person must do, then we are still under the fundamental premise of the Old Covenant, which is this: God’s blessing and favor depend on what we do. (This makes the cross of Christ of no effect.)
Faith is authored by Jesus; it is not a choice we must make. By definition, this means we play no causal role in believing in Him.
The “believing in Him” portion of John 3:16 implies that God has already acted within the human experience; its purpose is not to identify what a person must do to be saved. “Whoever believes in Him” describes the effect of hearing from God, which is the cause of eternal life. Hearing from God results in faith; it does not leave a person with the choice to believe or not.
John 3:17 – For God did not send His Son into the world to condemn the world, but so that the world through Him might be saved. (You cannot change the definition of the word “world” for only one of its uses.)
He who has ears to hear, let him hear.