#1. It's probably Goldberg's last match

In 2016, Goldberg proved the world wrong. He did have one last match left in him. If anything, he technically had four matches left in him, though the total time of those matches didn't last more than 10-12 minutes combined.
Either way, one can only hope that his match with The Undertaker is similar to Brock Lesnar at WrestleMania 33 - a chaotic, fast-paced and intense match that ends in a matter of minutes.
With that being said, it's quite clear that Goldberg won't wrestle again after this. Sure, he could do a Saudi appearance and get paid millions for it, but he's been very open about the fact that training at his age is extremely difficult, despite having consistently trained for years in retirement.
If it is indeed his last match, then Vince McMahon knows that the only way to go out is on his back - putting over The Undertaker.