Who was before a blasphemer, and a persecutor, and injurious: but I obtained mercy, because I did it ignorantly in unbelief.

No, nothing to do with that. It's because basically the entire thing is a church father pretending to be Paul and writing out a whole bunch of commandments for people to obey the church and never question the church, and how churches should be run. It also contradicts Paul pretty much every other sentence. Not that Paul has the right to institute such things in the first place.

Here are a few gems from it:

I urge, then, first of all, that petitions, prayers, intercession and thanksgiving be made for all people— for kings and all those in authority, that we may live peaceful and quiet lives in all godliness and holiness.

As if doing good only matters if it's towards kings and those in authority. Totally not an agenda or anything.

A woman should learn in quietness and full submission. I do not permit a woman to teach or to assume authority over a man; she must be quiet. For Adam was formed first, then Eve. And Adam was not the one deceived; it was the woman who was deceived and became a sinner.

Hmm, I wonder who's responsible for 1 Corinthians 11:3-16 and 14:34-35. This also disqualifies many people in the Bible itself, including Phoebe as a deacon and Junia as an apostle...who were associates with Paul.

But women will be saved through childbearing—if they continue in faith, love and holiness with propriety.

This statement is heretical on so many levels. First of all, this is a works salvation, stating that bearing children is a requirement for salvation for women (and probably men too, as we will see shortly). Not only that, but it treats celibacy or even not being able to have children as a sin, when celibacy is to be preferred--and Paul being one of its main proponents.

Here is a trustworthy saying: Whoever aspires to be an overseer desires a noble task. Now the overseer is to be above reproach, faithful to his wife, temperate, self-controlled, respectable, hospitable, able to teach, not given to drunkenness, not violent but gentle, not quarrelsome, not a lover of money. He must manage his own family well and see that his children obey him, and he must do so in a manner worthy of full respect. (If anyone does not know how to manage his own family, how can he take care of God’s church?)

Paul the celibate teaching that teachers must be married with children? I don't think so. By this law Jesus himself is condemned, and so is the apostle who supposedly gave it.

He must also have a good reputation with outsiders, so that he will not fall into disgrace and into the devil’s trap.

As if faith has ever been about having a good reputation with outsiders. More like the hypocrites clean the outside of the cup but are filthy inside, but happy are those who are persecuted and hated, because this is how the prophets and Jesus himself and all his followers were treated. Sounds like someone didn't like this and wanted to pressure believers back into obeying Roman social norms.

The Spirit clearly says that in later times some will abandon the faith and follow deceiving spirits and things taught by demons. Such teachings come through hypocritical liars, whose consciences have been seared as with a hot iron. They forbid people to marry and order them to abstain from certain foods, which God created to be received with thanksgiving by those who believe and who know the truth. For everything God created is good, and nothing is to be rejected if it is received with thanksgiving, because it is consecrated by the word of God and prayer.

This is targeted at Marcionism, which forbade marrying and eating meat. But the whole Marcion fiasco happened long after Paul's death. And based on the "certain foods, which God created to be received with thanksgiving by those who believe and who know the truth" language, we likely found the culprit behind the interpolation of 1 Corinthians 10:23-33.

Of course, I also find almost no interpolations at all in this letter. That probably means the church really didn't like what Paul wrote, so they rewrote him, and since this letter was authored entirely by themselves, there was no need for confusing interpolations everywhere.

I cannot find any reason for this letter to exist other than the most deceitful motivations. The author wants to keep believers in check and obeying the Roman empire and culture. He wants them to be submissive and like blind sheep, serving the authorities as much as possible. He wants to institute the Christian version of the Jewish temple religion of the Pharisees and Sadduccees. And we saw it happen throughout history, and it is still happening. This "letter" is flat-out heretical. I would not be surprised if the devil himself wrote it to confuse believers back into following religion and statism, so he can easily control them.