The promise you have fastened upon is the very word of God, and it stands sure. If you confess with your mouth the Lord Jesus and believe in your heart that God raised Him from the dead, you shall be saved. There is no “maybe” or “perhaps” about it; the Spirit of God has declared it, and He cannot lie. The resurrection of Christ is the mighty seal upon His finished work. It proves that the penalty for sin has been fully paid and that His righteousness is complete. When you believe that God raised Him from the dead, you are taking hold of a living Christ who has conquered death and hell for His people. His rising again is the verdict of heaven that the debt is canceled, so whoever believes on Him is free from guilt, even as Christ is free. Do not let the simplicity of this stumble you. The mind craves a complicated scheme, but God has condensed salvation into a line: confess with the mouth, believe in the heart, and you shall be saved.
Yet take careful heed: this faith is never a mere notion of the head. It is a grace that crowns Jesus as Lord of the heart and life. “Confess with your mouth the Lord Jesus”, that word “Lord” means Master, Sovereign, the autocratic Ruler of your entire being. No one truly believes on Him without submitting to His authority. If He has saved you from the guilt of sin, He has also delivered you from the dominion of it. Sin will still vex you and seek to regain mastery, but it shall not have dominion over you, for you are under grace. This is not work for salvation, it is the fruit of being saved. First believe, then obey. First receive life, then walk in the way. The root of all holiness is a trusting grasp upon Christ alone.
You mention the turning from sin and following Jesus. This is the indispensable mark of a genuine work, but see that you keep it in its right order. Salvation is of the Lord from first to last, He planned it, He executed it, and He applies it. You do not repent and reform in order to obtain Christ; you come to Christ just as you are, in your very desperateness, and He grants repentance as His gift. The way to heaven is indeed by Weeping-Cross, for he who never sorrowed for sin has never rejoiced in a Savior. But the sorrow flows from a sight of Him whom you have pierced, and the obedience springs from a grateful heart already at peace with God. Therefore, do not look within for any fitness of your own. Lay hold on God as Jacob grasped the angel, and do not let Him go until He blesses you. Cry out, “Lord, I am a broken, helpless worm, guilty and undone. I confess the Lord Jesus with my mouth, and I believe in my heart You raised Him from the dead. Save me according to Your word!”
Your advice to begin reading the Gospel of John is wise beyond measure. There the deity and grace of our Lord shine with noonday clarity. Read it as a hungry man devours bread, and as you read, cry to God for light. He will show you that simply to trust in Jesus is at once the safest and most suitable way of salvation. And as you find Him, your mouth will be filled with praise. True religion, from one end of life to the other, is praise, the heartfelt adoration of Him who called you out of darkness into His marvelous light. So seek Him in His Word, pour out your heart before Him in prayer, and expect a gracious answer. It is not possible that a sinner should sincerely seek mercy in God’s own appointed way and not find it. I sought the Lord, and He heard me, and delivered me from all my fears. What He did for me, He will do for you.