I want to cut the rebate or step out of an old door which has a glass panel this should give me room to fit a double glassed panel instead can i use a jig saw with guide or is this an excuse to buy a router?

I have worded this badly I actually want to remove the rebate leaving a flat surface .

Perfect excuse for a router.

If I’ve read what you want to do correctly then it’s a job for a router.

You need an excuse to buy tools?

Get a router but I should mention that if you’re a newbie to them like myself then the bearing guided router bits, as Kayak has posted, make life a lot easier (everything I own now has some sort of bevelled edge).

I would use a circular saw for that. Check on YouTube for how to make a simple fence which acts as a guide rail. Unless you have a really really good jigsaw (Festool) the cut will go all over the place.