[metmom]

You, I, St. Peter ans St. Paul will receive our bodies at the second coming of Christ. Mary however received her glorified body following her death.

And why? Why is this necessary?

Why is it so important to Catholics that Mary be considered sinless and perpetually virgin?

How does that affect the work of Christ on the cross?

What relevance does it have to said work?

[count-your-change]

Start pulling bricks from the tower of Babel and the whole thing might come crashing down.

[annalex]

reading way more into the passage than the context justifies.

Again, the context is words of dying Christ so the mutual adoption of the disciple and Mary has to have a greater significance than a mere economic arrangement. It is your side that ignores the context and the peculiarities of the wording. On this score, we just read what is written.

Chapter and verse? [for the assumption of Mary]

There is none; the Assumption of Mary is the teaching of the Church that is not in the scripture. For the obvious reason: the lives of saints are not the focus of it.

Why is it so important to Catholics that Mary be considered sinless and perpetually virgin?

It is important because it is true. It is a part of the saving faith. Is it logically important for some other dogma? I don't think so. But I am happy with the knowledge that Mary was singled out by God in this way.