Please demonstrate how you know empiricism to be true. Bear in mind that you are about to make an argument(s) from empiricist data, and that you are presupposing that empirical objects "exist".
Using metaphysics alone to demonstrate something's or someone's existence in reality, would only use use logic alone. People can use metaphysics that something or someone that actually exist, through naturalism.
But a religious believer, eg a theist, can argue a deity or deities exist, through his personal belief alone, using metaphysics, but his metaphysical stance is based on believing something that defy law of nature, hence this metaphysics would fall under the supernatural.
And there lies the problem with metaphysics. You don't require evidences or testings to substantiate claim of supernatural, like gods, spirits, angels, demons, jinns, fairies, or creatures like dragons, phoenixes, Griffins, cyclops, Pegasus, etc. For this very reason, metaphysics is useless, because anyone can argue for anything that don't exist, to be "real".
Metaphysics use just rationality alone. So both theists and non-theists can use metaphysics alone, and would not really get anywhere, because one could argue for his belief, while the other could argue for his disbelief, both sides cannot prove their claims, if they have nothing but their biased logic or biased belief.
This is the reason why I hate people, who simply use or rely on one philosophy.
If I am going to to say anything that's real, I would use more than one philosophy, to substantiate or verify my claim. I would use metaphysics, but I would mix this one philosophy with naturalism and humanism, and with empiricism, epistemology, ontology, pragmatism, logical-positivism, analytic philosophy, and with whole lot more.
But one of the best way to objectively verify anything or any claim, is using empiricism. Empiricism would allow me to repeatedly test claim, or to verify evidence with more independent evidences, in which I can conclusively settle any claim. This is not only to test for something that's true, BUT EVEN MORE IMPORTANTLY - to test if it is false.
Using rationality is all fine and well, but using rationality along with empiricism is much superior than using metaphysics.
Empiricism with falsification and scientific method is a better method of objectively verifying or REFUTING any statement regarding the natural world.
To me, religion is based more on the supernatural, which rely on people's ignorance and fear of the unknown. And there is a word for this...it is called "superstition". God's reply to Job, in JOB 38, 39, 40 & 41, demonstrate the bible reliance on faith and superstition in the supernatural. Nothing that God have said in those 4 chapters show God to be any more advanced than the primitive superstitious Iron Age people.
C'mon, man. The bible would have us believe that angels could have as many as one head with four faces or have as many as six wings...hence seraphim or archangels. If that's not superstitious nonsense, then what is it? Do we take this description of the seraphim, literally or metaphorically?
With humility, may I point out to you kindly that saying a source is not credible is actually slander until you provide evidence to the contrary. For example, there are three dozen Bible authors across 1,500 years, 9 for the NT alone. There are also 10 first century non-Bible historians who say things like "There are a bunch of Jews following Jesus, whom they say resurrected." Do you have contemporary documents proving the Bible authors were not credible or are you making an argument from silence?
The gospels are neither credible, nor reliable, historically-speaking.
The birth of Jesus, as narrated in 2 different gospels showed they are both unreliable, historically.
Now, I don't like Flavius Josephus as a historian, because he mixed biblical myths with his his history on the Jewish people, but he far more reliable with his history in the last 100 years (meaning from his time to 100 years before he began writing, so covering the 1st century CE and 1st century BCE).
Josephus doesn't provide any detail about Jesus, other than saying that James was his brother. But Josephus does include quite extensive details about the life of Herod the Great, and Herod's children (and descendants) as well as the war with Rome, during his own time. And in one of that chapter, Josephus included the execution of John the Baptist.
Neither Matthew, nor Luke - that if they were truly the authors of their respective gospels, clearly wouldn't have access to source materials that were available to Josephus.
For one, Josephus, came from noble family, and as well from priestly family. He was royally and priestly connected through his ancestry, so he had access to sources, like official documents from palaces and the temple, that neither gospel authors have. And being nobleman himself, he was far more educated than the average Jewish people.
Furthermore, he was connected to the Flavian dynasty, during the war with Rome, particularly with Titius, son of Vespanian.
Both Vespanian and Titius were commanders of the Roman armies in Judaea. When Josephus was captured, he defected to the Romans, and became their friend, and Titius' adviser.
My point in this historical background of Josephus' past, is that he, as a historian, would have access to official Roman records, as well as the the Jewish ones. He would have far more access to sources than any gospel author.
But getting back to your claim that the gospels were "credible", I have to say it isn't.
I stated earlier that the gospels about Jesus' birth are unreliable.
They not only conflict with each other, they are also historically unreliable.
With Matthew (gospel), we have the event about Herod. Like I said earlier, Josephus have materials unavailable to others, outside of nobility or royal family. And Josephus covered a lot about Herod's sordid life and his family (eg betrayal, corruption and murders), but none of them talk of Herod meeting 3 wise men, or that of ordering massacre of children in Bethlehem.
If the gospel was true about the massacre then Josephus wouldn't be silent on the subject, because Josephus have already quite extensively about Herod's tyranny. This is reason why I don't think the massacre happen.
Second, with regarding to the gospel of Luke, especially about the census of Quirinius. I think Luke, or whoever the hell was the real author, set the census at the wrong time, before Herod's death.
It is the wrong time, because Josephus clearly stated that the governorship and census of Quirinius didn't occurred (6 CE) until Archelaus lost his throne and was banished from Judaea, 10 years after the death of Archelaus' father.
Another inaccuracy of Luke's gospel is that Joseph had to travel from galilee to Bethlehem, to enrol in the census. The Romans wouldn't need to known a person place of birth or home town. They would enro (and pay their taxes) in the town they currently living in, eg Nazareth. The Romans wouldn't know or need to know what tribe Joseph belong to, because they bloody wouldn't care.
Can you image, several thousands of people travelling back to the towns they were born in?
It would be stupid, inaccurate and cumbersome for thousands of people travelling to other places to enrol in the census.