This is another question from my protestant friend.
If peter is the first Pope should not his teachings be based on scriptures, since through the inspiration of the Holy Spirit he penned the books of the bible?
And also did he not preach the first gospel message on the Day of Pentecost?
Well . . . there are only two books that are attributed to Peter, AFAIK. That would be 1 Peter and 2 Peter (which is not widely believed to have been written by him). The rest were probably not written by Peter. This is especially the case in say, the letters of St. Paul.
As far as whether his teachings were scriptural, I don’t know. I would want specific examples of what Peter taught that wasn’t scriptural.
On Pentecost, sure he preached what I might describe as the first Gospel message Peter preached after the Resurrection that has been written down. Does it mean it was THE FIRST Gospel message? No. Christ already covered that one. Does it mean it was the first Gospel message preached by Peter? Not necessarily. The disciples were commissioned to go and spread the Word before the Resurrection (Matthew 10). I highly doubt that Peter never spoke of Jesus during this little episode.
Even if Pentecost were the first time the Gospel message was spread, what does it matter? Is this somehow supposed to bring down the Catholic Church while building up the Protestants?
If Peter had a mother in law, then why can’t popes marry? That is another question from my non catholic friend.
Yes, he had a mother in law. It does not mean that:
(1) he was married at the time Jesus called him
(2) he was married at any point during the public ministry of the early Church
(3) that it has anything to do with current Church discipline.
The Church chooses to have celibate priests, bishops, and unmarried deacons. A number of the very early popes had wives and even children. Today, the Church has placed a rule that bars married men from the priesthood. The Eastern Churches (AFAIK) permit married priests, but not bishops. It’s all a discipline, and has nothing to do with the core of the faith.