Advice Needed Refurbishing Timber Interior Door

Hi all,
I am in the process of doing up our main bedroom and since the door was solid timber decided it might be worth doing up rather than painting, however I now find myself over my head. I have stripped off the several layers of paint and given it a rough sand with 80 grade to try and get an idea of what i'm working with. It is definitely solid timber but I have no idea if it is decent timber that will come up allright? I was planning on a varnish/stain finish to try and get that nice timber look.
As I have sanded I have found the timber has lightened dramatically, much more where I have sanded more (even though it was a fairly light sand). Would this mean it was previously stained? There are also some squiggly lines visible in the pictures that were there as soon as I started stripping the paint so I don't believe I caused them.
I have attached some pictures of when I had just started getting the paint off to where I am now, would really appreciate any advice on:
1. Is it worth continuing or would I be better off just painting it?
2. Where to now?

Cheers!

Images: Door - Imgur


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