The difference between Natural Faith and Supernatural Faith
Every normal human being is endowed with common sense, a kind of judgement that serves him to make ordinary decisions for his own good and welfare. For instance, by natural faith (even though we ordinary people cannot prove it scientifically) we like to drink milk because we believe it's good for our biological system; we embark a plane believing that the pilot and his crew are competent to take us to the desired destination. By natural faith I entrust the contents of an envelope in the hands of unknown postmen so that I may communicate with my friends abroad.
By contrast, supernatural faith is not granted to everybody indiscriminately, since it is a special gift which Christ has obtained by his death in order to bestow it upon his elect people. It is a divine blessing, unmerited and without which nobody can enter heaven, for by supernatural faith (engendered in us by the mysterious operations of the Holy Spirit) we are united to Christ and enjoy his redemption. This kind of faith, which the Bible recommends, is a gift of God (Philippians 1:29). It originates as one hears the Word of the Gospel, as a seed is sown into the ground: it germinates and takes root and sprouts. "So then faith cometh by hearing, and hearing by the word of God" (Romans 10:17).
By this faith we look beyond the reality of this present age and world. "Now faith is the substance of things hoped for, the evidence of things not seen" (Hebrews 11:1).
They apply to the individual in that while natural faith is needed to go on our daily run of affairs, and links us to society and the world around us, supernatural faith is indispensable for our right relationship with the living and true God. More than anything else, we need to cry out to God, "I believe, help thou mine unbelief." Being human we are born with natural faith; being born from above we are granted supernatural faith. For this latter kind of faith we are utterly dependent upon God.
The Conception of Faith
All men being born in Adam, are devoid of the life of God, alienated from Him and antagonistic to His purposes.
In mercy God seeks His wayward creature and brings him to Himself. This He accomplishes by a work of re-creation: He instils faith in the soul of man, so that man turns to Him in Christ and trusts Him for his whole salvation and entitlement to eternal life.
The conception of faith, therefore, refers to that exact moment in time when the Holy Spirit originates faith in man. To be sure, faith is exercised by man, and it's his responsibility to believe, yet he cannot do so without the implantation of faith within his heart. It is God-given: "For unto you it is given in the behalf of Christ, not only to believe on him, but also to suffer for his sake" (Philippians 1:29).
Use in evangelistic effort
In an sermon directed towards the lost, I would emphasise the need of coming to Christ, eating His flesh and drinking His blood, seeking refuge in Him (which are all figurative of believing in Him), and yet I would still point out that this is not a work they can do whenever they so desire. For the origination and exercise of faith, we all are wholly dependent upon God. "No man can come to me, except the Father which hath sent me draw him..." (John 6:44).
The Revelation of Faith
This concept can be fleshed out in the life-history of Saul of Tarsus, who, being converted, left it in writing that he "obtained mercy, that in me first Jesus Christ might shew forth all longsuffering, for a pattern to them which should hereafter believe on him to life everlasting" (1 Timothy 1:16). His case we must therefore consider as classical and exemplary for all of us.
The narration of his turning to Christ is found in three separate places in the Acts (ch.9,22,26). In all three instances special mention is made that Saul was a persecutor; he was not seeking God; he rejected God's Messiah as a blasphemous impostor, and in his self-righteousness he was gathering for himself wrath against the Day of wrath and revelation of God's righteous judgment.
And yet, in spite of his adamant opposition, Christ revealed Himself to his enemy and changed his course. Truly, as in all conversions: "I was found of them that sought me not; I was made manifest unto them that asked not after me" (Romans 10:20, quoting Isaiah 65:1,2).
In his blinding Saul was fighting against the Light; as soon as the Light shone upon him, the darkness was instantly banished. That is why, in proving that the gospel he preached was not man's invention, Paul the apostle refers us back to his former manner of life and then continues: "But when it pleased God, who separated me from my mother's womb, and called me by his grace, to REVEAL his Son in me..." (Galatians 1:15,16).
Unless God comes to us in mercy, we will never find him, for no man in his natural state seeks after God, being idolatrous in heart.
In bringing us to enjoy fellowship with Him through His Son, God makes use of his written revelation. Christ's words and deeds are "written, that ye might believe that Jesus is the Christ, the Son of God, and that believing ye might have life through his name" (John 20:31).