Preston:

1) Now, for the opening Point to you, you must understand, that there are two ways, or Covenants, whereby God offers salvation to men: One, is the Covenant of Works, and that was that righteousness by which Adam had been saved, if he had stood in his innocency; for it was that way that God appointed for him, Do this, and live: But Adam performed not condition of that Covenant, and therefore now there is another Covenant, that is, the Covenant of Grace; a board given against Shipwreck. Now this covenant of Grace is double:

Either absolute and peculiar,

Or conditional.

Absolute and peculiar only to the elect. So it is expressed, Jer 31. I will put my law in your inward parts, and write in your hearts, and I will be your God, and you shall be my people. So likewise in Ezech. 36. I will give you a new heart, and put a new spirit within you, and I will take your stony hearts out of your bodies. Here the Covenant is expressed absolutely, and this is proper only to the Elect.

But now, besides, there is a conditional Covenant of Grace, which is common to all; and that is expressed in these terms: Christ has provided a Righteousness, and Salvation; that his Work that he has done already. Now if you will believe, and take him upon those terms that is offered, you shall be saved. This I say belongs to all men. This you have thus expressed in the Gospel many places: If you believe, you shall be saved: as it is Mark 16. Go preach the Gospel to every creature under Heaven; he that will believe, shall be saved; and he that will not believe, shall be damned. It is the same with that, Rom. 4.5 To him which works not, his faith is accounted righteousness. (Mark it) To him that believes on him that justifies the ungodly; that is; there is a certain justice of righteousness, that Christ has prepared or purchased for men, though they be ungodly, he requires nothing of them before-hand, though they be wicked and ungodly, yet this righteousness is prepared for them: that which is required of them, is only that they take it.   John Preston, The Breast-Plate of faith and Love, (London: Printed by George Purstow, and are to be sold in the Companie of the Stationers, 1651), 30-33.

2) Object. 6.

It is objected that the Covenant that is made by God seems to be made with the elect only, and therefore the condition belongs only to them, how can Christ belong to all, seeing the exhortation and commandant must not exceed the Covenant, for the benefit is propounded to the Elect, and the condition to be required of none but of such as are within the covenant.

Answ.

To this I answer, that there is a Covenant of grace, and that is double, either a general covenant propounded without exception, “Let whosoever will come and believe in Christ shall be saved,” here is none excluded, and that none are excluded out of this general covenant this reason will show. Baptism the seal of the Covenant is to be administered to all within the Church, to infants though afterwards they do not actually and visibly believe. Now God would not appoint that the seal of the Covenant should be given to those whom it does not generally belong. But secondly, there is another Covenant of grace which belong peculiarly to the elect, for in this God does not only promise to give salvation, if men believed, but he promises to give them ability to believe, as may be seen, Jer, 31:33, Ezekiel 36. In the first place God promises that he will “put his law in their inward parts, and that they shall not teach any more every man his neighbor, but they shall all know me from the least to the greatest,” and so the life in other places, where God promises the thing, and ability of performing it, which belongs only to the elect. But the other general Covenant belongs to all without exception.  John Preston, Riches of Mercy to Men in Misery (London: Printed by J.T. and are to be sold by John Alen at the rising sun in Saint Pauls Church Yard),  425.  [Italics original, some spelling modernized, marginal references and headers cited inline, and underlining mine.]