这两个约就是行为之约和恩典之约，一个向那遵行律法上一切事的人应许永生，另一个向那些转向信靠基督的人应许永生。必须注意，保罗说，它们是两个，那就是在本质上或在类型上（in substance or kind）是两个。它们的差别有许多方面。律法，或称行为之约，提供的只是上帝的公义，没有怜悯；恩典之约，或称福音，既启示了上帝的公义又启示了上帝的怜悯，或者说上帝的公义让位于上帝的怜悯。第二，律法要求我们内在的完美的义，既是本性上也是行为上的；福音提供的是中保的义归算给我们。第三，律法应许生命的条件是行为；福音应许赦罪和永生的条件是我们通过信心依靠基督。第四，律法刻在石版上，福音刻在我们内心上（耶31:33，林后3:3）。第五，律法是通过创造存在于自然之中；福音则超于自然，在堕落之后被启示出来。第六，律法有摩西作中保（申5:27），而基督是新约的中保（来8:6）。最后，律法是用动物的血所立的（出24:5），而新约是用基督的血而立（来9:12）。
——威廉·珀金斯（William Perkins, 1558-1602），A Commentary on Galatians （《加拉太书注释》）, London: 1617, p.306
The two Testaments are the Covenant of works, and the Covenant of grace, one promising life eternal to him that doth all things contained in the law; the other to him that turns and believes in Christ. And it must be observed, that Paul says, they are two, that is, two in substance, or kind. And they are two, sundry ways. The law, or covenant of works, propounds the bare justice of God, without mercy; the covenant of grace, or the Gospel, reveals both the justice and mercy of God, or the justice of God giving place to his mercy. Secondly, the law requires of us inward and perfect righteousness, both for nature and action; the Gospel propounds unto us an imputed justice resident in the person of the Mediator. Thirdly, the law promises life upon condition of works; the Gospel promises remission of sins and life everlasting upon condition that we rely ourselves on Christ by faith. Fourthly, the law was written in tables of stone, the Gospel in the fleshy tables of our hearts. Jer.31.33. 2Cor.3.3. Fifthly, the law was in nature by creation; the Gospel is above nature, and was revealed after the fall. Sixthly, the law has Moses for a Mediator, Deut.5.27. But Christ is the Mediator of the new Testament. Heb.8.6. Lastly, the law was dedicated by the blood of beasts, Exod.24.5. and the new Testament by the blood of Christ. Heb.9.12.
Here then falls to the ground a main pillar in Popish religion, which is, that the law of Moses, and the Gospel, are all one law for substance; and that the difference lies in this, that the law of Moses is dark and imperfect, and the Gospel or the law of Christ more perfect: because he has (as they say) added counsels to precepts. Again, the law (they say) without the Spirit, is the law properly, and with the Spirit, it is the Gospel. But all this is false which they teach. For the two Testament the law and the Gospel, are two in nature, substance, or kind: and the difference lies not in the presence or absence of the Spirit.
— William Perkins, A Commentary on Galatians, London: 1617, p.306