I want to say there's a reason other than Nissa Nissa symbolism why team Stannis specifically chose the statue of the Mother to burn Lightbringer in.

The Mother is mercy and love, human emotions more powerful than the Red God's magics. Of course he who was notoriously without mercy would choose her over the Maiden to be his Nissa Nissa to bring forth Lightbringer

Stannis's whole persona is built around a lack of mercy and the absence of love, by burning his great flaming sword in mercy herself, he is demonstrating his conquest of love and mercy. If he can't have them, he can at least master them.

But he can't, not truly. Stannis fumbles the ceremony, burning himself and singeing his oven mitt. I think his fumble isn't just a sign that he isn't the hero, but also a sign that he is still a man with a little nugget of a soul, and he can't conquer mercy.

But he keeps trying to conquer it- killing Renly, trying to kill Edric, eventually killing Shireen- but he can't, and it's physically killing him