2. Under the new covenant or testament, however, these promised blessings are not given to all men, because God is true, thus the covenant is necessarily discriminate. These blessings are, however, given doubly when the covenant is received. In the first place, by the substance itself of the covenant, or by the promised blessings from God themselves, then by their administration in the visible assembly. In the first meaning learned from Jeremiah in the place already cited and which substance is peculiar to the elect.
For to all the elect and to them alone, this part, the remission of sins, renewal to the image of God, and the knowledge of God itself is therefor promised, or which embraces God’s favor which they would never have had from themselves (John 6:44,45; 64,65; 10:26; 11:52; Acts 13:47,48; Romans 8:29,30; 9:7,8,9,11,15,16; Titus 1:1).
Thus Moses spoke about substance of the covenant (Deuteronomy 30[:6]). “God will circumcise your heart and that of your children.” He acts truly in the administration of the covenant, (Genesis 17), ‘This is my covenant’ etc. Likewise he says, ‘My covenant will be in your flesh.’ Certainly, the very substance of the covenant was not in their flesh. And not all of their hearts were circumcised, to whom the covenant was administered or offered through circumcision (Acts 7:51,52,53). That is to say, they personally, maliciously, rejected the gracious offer of the covenant, as Stephen teaches in the same place. Therefore, the covenant of grace, if you see its essence, is a sworn oath promised by God, a gift to you by God who who is never angry with you (Isaiah 54) and by our adoption in God’s Son we have been made heirs of eternal life with Jesus Christ the eternal and only begotten Son of God, the seed of Abraham who is Christ, and to all men, who by faith in this free gift which was brought by the seed, and in whom by grace they were justified and glorified short of any condition or stipulation, knowledge of the good, so that he might be celebrated in his gracious goodness from himself, in this life and life eternal (Hosea 2; Isaiah 54; Genesis 22; Hebrews chapters 1, 6; Galatians 3:15-18, 22,26,29).
The administration of the covenant of grace, however, is through the testimony or call of the Royal word from the darkness (of which darkness he is convicted by the law partly natural and partly written) that is, from sin and the penalty of sin, to the light, which is unto the discerning and receiving of the Son of God offered in the gospel, with the double benefit, truly, free rightousness in the remission of sins, by cleansing in his blood, and renewal to the image of God or the spirit of holiness for sharing in the heavenly inheritance.
By the outward voice and visible signs in the testimony of mutual agreement between God and us, and by the addition of the truly efficacious gift of grace of internal faith and repentance out the infinite, incomprehensible mercy to the elect, which mercy is not truly added indeed to the reprobate, but nevertheless justly and to the worship of God’s justice. For the call from the darkness to the light, that is, the gracious offer, is never rejected without evil and contumacy of the heart.
Caspar Olevianus, De substantia, 1.1.2