Then went in also that other disciple, which came first to the sepulchre, and he saw, and believed. For as yet they knew not the scripture, that he must rise again from the dead. (St. John 20:8-9)
I had always wondered about these verses, until today, when I ran across an explanation from St. Augustine which makes a lot of sense. He says that the words "he saw, and believed" refer merely to what the women had reported, namely "They have taken away the LORD out of the sepulchre, and we know not where they have laid him" (v2). Hence, what "they believed" was not the truth, but only the report which was a deduction from reason.
They believed what was not true, until Christ Himself corrected their false belief with His word.
St. Augustine's explanation explains why it says after "they believed" that "as yet they knew not the scripture, that he must rise again from the dead."
And this in turn leads us to pay heed to the Scriptures, lest we likewise believe falsehoods on the basis of deduction from reason.