"The two testaments are the covenant of works and the covenant of grace, one promising life eternal to him that does all the things contained in the law, [and] the other to him that turns and believes in Christ."

The two testaments are the covenant of works and the covenant of grace, one promising life eternal to him that does all the things contained in the law, [and] the other to him that turns and believes in Christ. And it must be observed that Paul says, 'They are two,' [a reference to Galatians 4:24- J.F.) that is, two in substance or kind. And they are two sundry ways.

[First] 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 pormises remission of sins and life everlasting upon condition that we rest ourselves on Christ by faith.

Fourthly, the law was written in tables of stone; the gospel, in the fleshly tables of our hearts (Jer. 31:33; 2 Cor. 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 (Ex. 24:5); and the New Testament, by the blood of Christ (Heb. 9:12).

William Perkins, The Works of William Perkins, 2:302-303