John Owen concludes his excellent Preface with these words:
"This worthy author has laboured, if I am not much mistaken, unto good success. And, as his design is to extricate things which seemed perplexed, to give light into the whole doctrine of the covenants, by declaring the proper order and method of things contained in them, with their respect one unto another; that the grace of God, in the Covenant of Grace, may be exalted, and his faithfulness, with his holiness, in the Covenant of Works, both in and by Jesus Christ, the end of the one, and the life of the other. So the reader will find, I hope, that satisfaction in these great and deep enquiries, which he will have occasion to return praise and thanks to God for."

Mark Jones concludes his excellent New Introduction with these words:
"The rewards are to be reaped from a careful study of this work. I would suggest keeping a Bible and pencil close by since Petto is constantly making reference to the Scriptures without giving the quotation of the passage cited. But more importantly, I would suggest keeping your heart firmly fixed upon the Lord Jesus Christ as he reveals to you, by his Spirit, THE GREAT MYSTERY OF THE COVENANT OF GRACE."