The “Covenant of Grace” is a teaching within the Westminster confession of Faith and the Catechisms that systemetizes and explains core Christisn beliefs. The “Covenant of Grace” consists of the Old and New Testament. They are not two covenants but one. The Old Testament of “time of the law” and the New Testament or “time of the gospel” are different administrations within the “Covenant of Grace.” The Westminster Confession of Faith states:
This covenant of grace is frequently set forth in Scripture by the name of a testament, in reference to the death of Jesus Christ the Testator, and to the everlasting inheritance, with all things belonging to it, therein bequeathed.Westminster Confession 7.4
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.Westminster Confession 7:5
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 SupperWestminster Confession 7:6
Below is an Infographic explaining this concept.