The covenant of works being broken by sin, and made unprofitable unto life, God was pleased to give forth the promise of Christ, the seed of the woman, as the means of calling the elect, and begetting in them faith and repentance; in this promise the gospel, as to the substance of it, was revealed, and [is] therein effectual for the conversion and salvation of sinners.
Gen 3.15, Rev 13.8
This promise of Christ, and salvation by him, is revealed only by the Word of God; neither do the works of creation or providence, with the light of nature, make discovery of Christ, or of grace by him, so much as in a general or obscure way; much less that men destitute of the revelation of Him by the promise or gospel, should be enabled thereby to attain saving faithor repentance.
Rom 1.17, Rom 10.14-Rom 10.15, Rom 10.17, Prov.29.18, Isa 25.7, Isa 60.2-Isa 60.3
The revelation of the gospel unto sinners, made in divers times and by sundry parts, with the addition of promises and precepts for the obedience required therein, as to the nations and persons to whom it is granted, is merely of the sovereign will and good pleasure of God; not being annexed by virtue of any promise to the due improvement of men’s natural abilities, by virtue of common light received without it, which none ever did make, or can do so; and therefore in all ages, the preaching of the gospel has been granted unto persons and nations, as to the extent or straitening of it, in great variety, according to the counsel of the will of God.
Ps 147.20, Acts 16.7, Rom 1.18-Rom 1.32
Although the gospel be the only outward means of revealing Christ and saving grace, and is, as such, abundantly sufficient thereunto; yet that men who are dead in trespasses may be born again, quickened or regenerated, there is moreover necessary an effectual insuperable work of the Holy Spirit upon the whole soul, for the producing in them a new spiritual life; without which no other means will effect their conversion unto God.
Ps 110.3, 1 Cor 2.14, Eph 1.19-Eph 1.20, John 6.44, 2 Cor 4.4, 2 Cor 4.6