Quick overview (one sentence): The writer says that because he must discuss the duties/boundaries of both the earthly and heavenly city, he will first set out the arguments that non‑Christians used to try to make themselves happy in this life, so that we can see how our hope differs from their empty hopes and so that true blessedness (which God will give) may be made clear not only by divine authority but also by reason.
- Level 1 — Key words and simple meanings (vocabulary and forms)
- Quoniam — "since" or "because" (introduces a reason).
- de civitatis utriusque — "about the two cities" (utriusque = "of both").
- terrena scilicet et caelestis — "namely the earthly and the heavenly."
- debitis finibus — "proper/due limits" or "proper duties/boundaries."
- deinceps — "from now on" or "next."
- mihi uideo disputandum — literally "to me it seems that there is something to be discussed" ("disputandum" = a verbal noun/gerundive idea: "must be discussed").
- prius exponenda sunt — "first must be explained/set forth." (exponenda = things to be explained; sunt = they are/they must be.)
- quantum ... patitur — "as much as ... allows." (quantum = how much; patitur = allows/tolerates.)
- argumenta mortalium — "the arguments of mortals (non‑Christians)."
- quibus ... moliti sunt — "by which they tried/attempted" (quibus = abl. pl. referring to "argumenta").
- sibi ipsi beatitudinem facere — "to make/obtain happiness/blessedness for themselves."
- in huius vitae infelicitate — "in the unhappiness/misery of this life."
- ut ... quid differat — "how/ in what way it differs" (differat = subjunctive form of "differre").
- res ipsa, hoc est vera beatitudo — "the thing itself, that is, true blessedness."
- quam dabit — "which he will give" (dabit = future of "dare").
- non tantum ... sed etiam — "not only ... but also."
- auctoritate divina — "by divine authority."
- adhibita etiam ratione — "by reason applied as well."
- clarescat — "may be made clear" (subjunctive showing purpose/result: "let it be made clear").
- Level 2 — Grammar and important forms (what each form does)
- "Quoniam ... deinceps mihi uideo disputandum": Quoniam starts a reason. "Mihi uideo" is an impersonal feeling/seeing construction: "it seems to me." "Disputandum" indicates there is something to be argued/discussed (a gerundive/gerund idea of necessity).
- "prius exponenda sunt argumenta mortalium": exponenda sunt = passive periphrastic sense ("must be set forth"). "Argumenta mortalium" is the subject (what must be set forth).
- "quantum operis huius terminandi ratio patitur": a clause of extent introduced by "quantum" (= "how much/as far as"), with "operis huius terminandi" as a genitive phrase modifying "ratio" (the plan/measure for finishing this work). "Patitur" = "allows/permits".
- "quibus ... moliti sunt": "quibus" refers back to "argumenta" and is ablative plural ("by which"). "Moliti sunt" is a deponent perfect = "they tried/undertook." The object of their trying is "sibi ipsi beatitudinem facere."
- "ut ab eorum rebus vanis spes nostra quid differat quam deus nobis dedit": "ut ... differat" introduces a clause expressing result or an indirect question in purpose sense — "to show/so that we may know how our hope differs from their vain things compared with what God gave us." "Dedit" is perfect/has given (here future meaning earlier used as present context? but translated as "gave/has given").
- "res ipsa, hoc est vera beatitudo, quam dabit, clarescat": the writer wants the "thing itself (true blessedness which God will give)" to be clear. "Clarescat" is subjunctive: "may it be made clear."
- Level 3 — Clause structure and how the pieces fit together
- Main idea (line 1): Because I must discuss the two cities' proper limits, I see that discussion is necessary. (Quoniam ... deinceps mihi uideo disputandum.)
- Plan step 1 (line 2): First, something must be explained: the arguments of mortals, as far as the plan for finishing this book allows. (prius exponenda sunt ... argumenta mortalium ... quantum ... patitur.)
- Explanation of those arguments (line 3): These arguments are the ones by which they tried to make themselves happy in life's misery. (quibus ... moliti sunt.)
- Purpose/result (line 4): The point of setting out those arguments is to see how our hope differs from their vain things and how it compares with what God gave us. (ut ... quid differat ... quam deus nobis dedit.)
- Conclusion/purpose continued (lines 5–6): The writer wants the thing itself — true blessedness which God will give — to be made clear, not only by divine authority but also by reason the writer can use because of unbelievers. (res ipsa ... clarescat; non tantum ... sed ... adhibita ratione ... clarescat.)
- Level 4 — Translations and interpretation
Literal, line‑by‑line (keeps word order):
1) Since about the two cities, namely the earthly and the heavenly, concerning their proper limits/duties, henceforth it seems to me that there must be discussion; 2) first must be set forth, as much as the plan for finishing this work allows, the arguments of mortals 3) by which they themselves tried to make blessedness for themselves in the unhappiness of this life, 4) so that it may be known how our hope differs from their vain things and what it is that God gave us, 5) the very thing itself, that is true blessedness, which he will give, 6) may be made clear not only by divine authority but also by reason applied, of the sort which on account of unbelievers we can apply.
Smooth, natural English translation:
Because I must discuss the proper limits of both cities — the earthly city and the heavenly city — it now seems to me that I should begin. First I must set out, as far as the plan for finishing this work allows, the arguments of non‑Christians. These are the arguments by which they tried to secure happiness for themselves despite the miseries of this life, so that we can see how our hope differs from their empty hopes and how the true blessedness that God will give us stands apart. I want that very thing — true blessedness, which God will give — to be made clear not only by divine authority but also by reason of the kind we may use when addressing unbelievers.
Short interpretation / why the writer does this: The author plans to compare pagan or secular ideas of happiness with the Christian hope. He will first fairly present the non‑Christian arguments (so readers see them), then show how Christian hope and the true gift of blessedness from God differs, and he will support the Christian view both by scripture/divine authority and by reason (so arguments also work when talking to non‑believers).
Tips for studying similar Latin sentences (for a 13‑year‑old):
- Find the main verbs first (here: uideo, exponenda sunt, moliti sunt, dabit, clarescat). They show the main actions or goals.
- Look for relative words (quibus, quam) and connectors (quoniam, ut, sed). They tell you how clauses are joined (reason, purpose, contrast).
- Gerundives/gerunds (like exponenda, disputandum) often show necessity or things to be done — translate as "must be ..." or "to be ..."
- Subjunctive verbs (differat, clarescat) often mark purpose or result in these kinds of texts — translate with "may/let" or "so that ..."
If you want, I can mark each Latin word with its part of speech and grammatical role (subject, object, case, tense) right under the original lines so you can practice parsing each word.