Another passage on the “Sinaitic legal covenant” that perhaps could be a little clearer in Giger’s translation.
This is paragraph 24, the penultimate paragraph in the section.
First, here is Giger:
“The promise of the land of Canaan given to the people was not primary and principal, but only secondary and less principal (add by way of proposition [prothekes]; of addition to the primary concerning God about to be their God and indeed as a pledge and symbol of the heavenly Canaan [of which it was a type, Heb. 4], to which the fathers looked [Heb. 11:15, 16]). Therefore, a specific diversity of covenant cannot (except falsely) be inferred from the diversity of that promise from the one given to us in the gospel. Rather only a diversity of dispensation may be inferred which even the other differences between the Old and New Testaments here adduced concerning the spirit of bondage (of which we have spoken before) imply.”
Now, the Latin:
Cum Promissio terrae Canaan data Populo non fuerit primaria et principalis, sed tantum secundaria et minus praecipua, addita per modum προθήκης; accessionis ad primariam de Deo futuro ipsius Deo, et quidem in pignus et symbolum Canaanis Coeliestis, cujus erat typus, Heb. iv., ad quam Patres respiciebant, Heb. xi. 15, 16; Non potest nisi perperam ex diversitate istius promissionis ab ea, quae nobis datur in Evangelio, colligi diversitas specifica foederis, sed tantum diversitas dispensationis, quam inferunt etiam alia discrimina, V. et N.T. quae hic afferuntur de Spiritu servitutis, &c. de quibus supra dictum est.
Now, a revised translation with notes that I hope will make the sense clearer, even if more of syntactical complexity has been retained:
“Since the promise of the land of Canaan was given to the people not as the primary and principal [promise], but only as a secondary [promise] and not the chief one1, added in the manner of a prefix–[that is, in the manner] of an addition to the primary promise concerning God–that He would be the God of [the people] itself;2 and [it was added] also for the purpose of a pledge3 and symbol of the heavenly Canaan–of which [the earthly Canaan] was a type (Heb. 4)–to which4 the Fathers were looking (Heb. 11:15-16): [since all of that is the case],5 it is not possible that, from the difference of that promise6 from the one that is given to us in the Gospel, a difference of covenant as to species7 be inferred, except erroneously, but only a difference of dispensation8–[a difference] that is also introduced by other distinctions that are adduced here between the Old and New Testaments concerning the spirit of slavery, etc. About these things I have spoken above.”
- Giger uses “principal” to translate both principalis and praecipua. The words are basically synonymous, but I have attempted to preserve Turretin’s variatio.
- Thus the promise of the land is annexed secondarily (and probatively–see  below: it is a proof or assurance of the acquisition of the heavenly Canaan) to the real heart of the covenant (“I will their God, and they shall be my people”), which is also the substance of the Abrahamic covenant and the New Covenant.
- A pignus is a pledge, security, proof, or assurance of/for something else.
- That is, to the heavenly Canaan. The earthly promised land is typological of the heavenly promised land; and so it stands to reason that they are acquired in the same way: by the promise and gift of God.
- The preceding forms one long causal clause, and we now come to the main clause. I have added a resumptive “since” to clarify the structure.
- That is, the one relating to the land.
- Giger translates as “a specific diversity,” but this strikes me as awkward and obscuring, at least for the reader of modern English. The adjective used, specifica, is used precisely as a compound adjectival form of the noun species, which Turretin employs throughout this section in order to deny that the Mosaic administration was a covenant of a different “species” (species) from the one referred to in the New Testament.
- Or “economy.”