For a man who has the Old Testament put into his hands, which contain prophecies, and the New Testament afterward, which is said to contain their completions, and is once satisfied, as he may be with the greatest ease, that the Old Testament existed before the New, may have a complete, internal, divine, demonstration of the truth of Christianity, without long, and laborious enquiries.

Whereas, arguments of another nature, such, for instance, as relate to the authority and genuineness of the books, and the persons, and characters of authors, and witnesses, require more application, and understanding, than falls to the share of the bulk of mankind; or else are very precarious in themselves, since we know that in the first centuries there were numberless forged Gospels, and Apocryphal writings imposed upon the credulous as apostolic and authentic; and there were in the Apostles times, as many, and as great heresies and schisms as perhaps have been since in any age of the Church.

So that, setting aside the before mentioned internal proofs from prophecy, (which were the Apostle's proofs and in their nature sufficient of themselves) we should have no certain proof at all for the Religion of the New Testament.
On the other hand, if the proofs for Christianity from the Old Testament, are not valid, if the arguments founded on that Book be not conclusive, and the Prophecies cited from thence be not fulfilled, then has Christianity no just foundation; for the foundation on which Jesus and his Apostles built it is then invalid, and false.

Nor can miracles, said to have been wrought by Jesus, and his Apostles in behalf of Christianity, avail anything in the case.

For miracles can never render a foundation valid, which is in itself invalid; can never make a false inference true; can never make a prophecy fulfilled, which is not fulfilled; and can never designate a Messiah, or Jesus for the Messiah, if both are not marked out in the Old Testament; no more than they could prove the earth to be the sun, or a mouse a lion.
Besides, miracles said to have been wrought, may be often justly decided false reports, when attributed to persons who claim an authority from the Old Testament, which they impertinently alledge to support their pretentions.