Letter and Spirit

Westminster Confession of Faith 7:4-6
4.
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.
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 fore-signifying 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 fulness, 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.