Because it shows the shift from small local churches to a monolithic Katholikos ecclesia (Universal or Catholic church) with ecclesiastical doctrine that wasn't supported by (then) existing texts.
In the 2nd and 3rd centuries, the first writings weren't 'Holy Scripture' as the Jews would call it. Based on what has been recovered from the Dead Sea Scrolls at Qumran, the Jewish scribes were remarkablely faithful in copying what they considered 'Sacred writings'.
In contrast, the early Gentile redactors felt free to add, change, or delete whole passages if it suited the church's developing dogma.
The long conclusion of Mark 16:9-20, John 8:3-11, (the adulterous woman), Acts 8:37-38 (the baptism of the Ethiopian), I John 5:7-8 (the Johannine Comma), the obscuration of the 'Beloved Disciple' in John, etc. all show the hand of a redactor. It wasn't until the 5th century that the texts became unalterable 'scripture'.
In the case of the Pastoral Epistles, they were made out of whole cloth and attributed to Paul to give them authority.
The Pastorals justified (a coincidence, I'm sure) the Church's suppression of the local churches on the basis of 'false teachings'; Gnostic at first, then the heresy of Arius, then later still the wholesale massacre of Cathars.
"Now keep on following the Law....."
Wow...very interesting! May I ask how you qualified these assertions?