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The word of God is that word which came from God himself.
The first words of God were uttered in Eden. A blessing and a prohibition. Then, following disobedience, a judgment. But also a promise.
There followed other words of God spoken to individuals. To Noah, to Abraham, to Moses, to the prophets.
Paul the apostle leans heavily on these records for his doctrine. The question's statement 'Paul's source for his scripture is divine revelation only' is not true, without some qualification.
Reading the epistles, Romans and Galatians and Colossians particularly, his every reference in doctrinal matters is to the law of Moses and the prophets of Israel : to the recorded words of God himself.
Then, the words of Jesus are presented by four evangelists. Upon these words, more doctrinal teaching is built, particularly by Peter and by John.
The idea that Luke used Mark and Josephus as references is sheer supposition. And there is no evidence whatsoever that the document called 'Q' ever existed.
We should pay heed to the writers who are chosen vessels, given especial gifts by God himself in order for God to present his own words to us.
This is the word of God. It is his utterance, through chosen vessels. And it is kept in Divine Providence, supplied in thousands of manuscripts which can be collated together, scientifically, in a reliable documentation that can be trusted.
These are the 'God-breathed' scriptures. Holy words. Divine in origin.