Maybe to increase religious tensions? He was very anti-muslim, and hated germany for enabling “islamization of europe”.
So probably in his mind, if he, being saudi, were to attack a christian related event just before the election, it would snowball into some anti-muslim winning election thus him getting what he wanted.
He had a website to help women escape Saudi arabia, due to state oppression. He had issues with German state not doing much to stop the spread of islam in germany. He claimed Germany is enabling “islamization of europe”.
For context, in may 2024 there was a anti-islam rally, and a refugee tried to attack them and ended up attacking a police officer and killing him. This culminated in a historic rise of anti-islam and anti-immigrant AfD. And they won the state election in Thuringia in September.
Germany currently has federal elections in February, this attack was an attempt to incite anti-islam sentiment again just before the election.
He was pro-immigrant for ex-muslims, but anti-immigrant for muslim ones (which happen to be the majority).