Clearly you are trying for something more when you point out this alleged "nonsensical" in the Bible, but I guess the world will never know.
If by that you mean, I would like a better explanation than the frivolous excuses and responses than have already been offered then you are correct.
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The fact is, John was baptising people and had not been baptised himself. Jesus was baptised when he was sinless. Why? and no one can say what it was he had to repent for.
John says he didn't know Jesus was the messiah until he saw the sign of the dove, that confirmed to him he was gods son!! Then had second thoughts about his messiahship. he saw the ecending dove a message from gos and then had second thoughts!!? There are many inconsistencies when it comes to the story of John the baptist.
None of his story makes any sense as it has come down to us via the scriptures.
Why didn't Jesus resurrect John said to be the greatest prophet? What happened to him when it is said he had been killed on the whim of a woman via her mother, a woman (a key player) that is not even named in the gospels as the one being responsible for the death of the greatest prophet?
Why does it appear that the gospel writers want to keep this woman's identity secret?.
They do this often including when it comes to very relevant and important figures that play key roles in the death of Jesus and christianity as a faith..
One minute John is dead and then alive and then dead again
by being beheaded. How many heads did he have?! How many times did he die?
It seems to me you/belivers don't want to recognise these ambiguous statements in the bible and would rather not be challenged on them because they are not consistent with what you want to, and prefer to believe.
These simple and obvious questions should be simple enough for any believer to answer given that there has been 2,000 years to come up with reasonable answers.
The truth is as you say "the world will never know", but this won't stop the religious believer peddling what they want to believe as gospel truth,and has left the whole subject of christianity open to nothing but assumption, conjecture and guessing.
All my opinion, of course.