5. This covenant was differently administered in the time of the law, and in the time of the gospel: 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; 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, by whom they had full remission of sins, and eternal salvation; and is called the old testament.
6. Under the gospel, when Christ, the substance, was exhibited, the ordinances in which this covenant is dispensed are the preaching of the Word, and the administration of the sacraments of baptism and the Lord’s Supper: which, though fewer in number, and administered with more simplicity, and less outward glory, yet, in them, it is held forth in more fullness, evidence and spiritual efficacy, to all nations, both Jews and Gentiles; and is called the new testament. There are not therefore two covenants of grace, differing in substance, but one and the same, under various dispensations.
WLC Q&A 33-35
Q. 33. Was the covenant of grace always administered after one and the same manner?
A. The covenant of grace was not always administered after the same manner, but the administrations of it under the Old Testament were different from those under the New.
Q. 34. How was the covenant of grace administered under the Old Testament?
A. The covenant of grace was administered under the Old Testament, by promises, prophecies, sacrifices, circumcision, the passover, and other types and ordinances, which did all foresignify Christ then to come, and were for that time sufficient to build up the elect in faith in the promised messiah, by whom they then had full remission of sin, and eternal salvation.
Q. 35. How is the covenant of grace administered under the New Testament?
A. Under the New Testament, when Christ the substance was exhibited, the same covenant of grace was and still is to be administered in the preaching of the word, and the administration of the sacraments of baptism and the Lord’s supper; in which grace and salvation are held forth in more fullness, evidence, and efficacy, to all nations.