Accidental truths of history can never become the proof for necessary truths of reason.
I don't recall when I first read Lessing's Ditch. It was many many years ago. There are still village atheists who promote this dichotomy.
i) The dichotomy is overstated. Take the statement that every red object is a colored object. That's a necessary truth about a contingent object.
ii) Making allowance for his overgeneralization, Lessing's statement is often true. But how is that relevant to Christianity?
The implication is that unless Christian doctrines are necessary truths, they don't warrant our credence. But that's a non sequitur.
For one thing, truths about the nature of God are necessary truths. God is not a contingent being.
iii) Lessing fails to distinguish between word-media and event-media. Although the Christian faith is based in part on historical events, it is also based on divine revelation, including the inspired interpretation of redemptive events.
So even if the event is an "accidental truth of history," it doesn't follow that revealed truths about God, or even revealed truths about redemptive events, are accidental truths of history.
In general, our knowledge of Christian doctrine derives, not from historical events directly, but from historical records of historical events. That's not something we inferred from observing the event.
iv) There's nothing defective about truths of fact in contrast to truths of reason. Truths of fact are just as true as truths of reason. It's simply adapted to the nature of the object. If you have contingent events, you have corresponding truths of fact. There's nothing deficient in that relation.
v) But Lessing might object that truths of fact don't warrant the same degree of certainty as truths of reason. To begin with, that's an overstatement, as I demonstrate under (i).Likewise, take self-presenting states (i.e. introspection). Although my mental states are contingent, I know what I'm thinking.
vi) Ultimately, though, it's up to God to put us in situations where we form our beliefs from a reliable process. Certainly God can do that.