A persuasive promise to Christians by evangelists is the simplicity of receiving Christ and of salvation, which is quoted in the Bible: "That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved."(Rom 10:9) The persuasion seems just a matter of the heart; that if our confession is really true in our heart, then we are saved!
But let anyone be not ignorant that the Devil himself believes, and even trembles, so what makes us differ to the Devil? (James 2:19)
Peter was willing to give his life for Christ, but at one time, his faithfulness to serve Christ from harm was the reason of Christ calling him Satan! (Matt 16:21-23). Peter rejects that Christ is fated to be killed. But Israel's rejection of Christ that lead to his crucifixion was God's will. In fact, Christ himself prayed that the cup, referring to what he will suffer, be taken from him. (Mark 14:36) Peter's error implies that it is important for us to know God's will. Christ said, "Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven."(Matt 7:21) Peter did not know God' s will about Christ's rule in the Calvary at that time. Objecting for Christ to suffer in the Calvary makes him not submitting to God's will.
Let us learn from this story of Peter. Let everyone learn that following blindly would not save us, and rather leads unto a wide and easy path leading to our destruction. In fact, Paul was even sorry for some Jews, who, in spite of their zeal of God, had failed in righteousness because of lack of knowledge. (Rom 10:1-3)
The faith that saves comes by hearing the word of God. (Rom 10:17) It is a faith that come through intellectual assent. (Gal 3:23-25) For to have eternal life is to know God through Christ. (John 17:3, Matt 11:27, John 1:18) The light of the gospel that is being preached unto us for to know God through Christ:
5 For we preach not ourselves, but Christ Jesus the Lord; and ourselves your servants for Jesus' sake. 6 For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ. 2Cor 4:5-6
So what is being being shown unto us in the Gospel of Christ is the knowledge of godhead, and which this gospel is hid unto the lost. (2Cor 4:3-4)
How great the mystery of the gospel is that we, who have come to know it, were now free from the condemnation, being freed from the law of sin and death. (Rom 8:1-2) And thus, for us who known the truth are no more under sin. (Rom 6:14, John 8:32-34) And that for those who still have conscience of sin would meant that ignorance of God. (1John 3:5-6).
True faith does not stand in the wisdom of men, but in the wisdom of God's power. And that it is a mystery that is revealed to us through the Spirit. (1Cor 2:5-10) And thus, Paul said: "....no man can say that Jesus is the Lord, but by the Holy Ghost." (1Cor 1:3). This meant that true confession is done, or possible, only after we receive the revelation of the mystery of Christ by the Spirit/Holy Ghost.
For one to claim of having faith, but have no knowledge of the mystery of sin, or other mysteries, such person is lying, and a deceiver; or is deceived himself. They are the people who call Jesus Lord, but lack knowledge of the mystery of the godhead, and consequentially are not able to do God's will.