WLC Q.34: How was the covenant of grace administered under the Old Testament?
The covenant of grace was administered under the Old Testament, by promises, (Rom. 15:8) prophecies, (Acts 3:20,24) sacrifices, (Heb. 10:1) circumcision, (Rom. 4:11) the passover, (1 Cor. 5:7) and other types and ordinances, which did all fore-signify Christ then to come, and were for that time sufficient to build up the elect in faith in the promised Messiah, (Heb. 8,9,10,11,13) by whom they then had full remission of sin, and eternal salvation. (Gal. 3:7–9,14)
WCF 7.5.
This covenant was differently administered in the time of the law, and in the time of the gospel: (2 Cor. 3:6–9) under the law it was administered by promises, prophecies, sacrifices, circumcision, the paschal lamb, and other types and ordinances delivered to the people of the Jews, all foresignifying Christ to come; (Heb. 8–10, Rom. 4:11. Col. 2:11–12, 1 Cor. 5:7) which were, for that time, sufficient and efficacious, through the operation of the Spirit, to instruct and build up the elect in faith in the promised Messiah, (1 Cor. 10:1–4, Heb. 11:13, John 8:56) by whom they had full remission of sins, and eternal salvation; and is called the old Testament. (Ga. 3:7–9, 14)