Getting partner on board

Hi Brooke!
So, I moved into my partner’s house last January and I can’t even tell you how much shit is all over this place. Major clutter. I have begun cleaning out this spare room that’s being totally unused. It may become either his office or my “get ready room”. Either way, I brought up the possibility that a cluttered house could mean a cluttered mind and he didn’t agree with me entirely and that’s ok. I want him to move at his own pace and not push him but how do I get rid of stuff when he resists? I used to be a hoarder but slowly, over the past few years, I’m learning that stuff is just stuff and I can readily let things go. He says that when stuff is packed in the back of a closet, it’s like out of sight out of mind. I totally disagree with this because it just means there’s stuff going on in your mind that you are perhaps ignoring. I really want to get this house cleaned up so how do you suggest I go about this? By the way, I have a nice pile in this room for him to go through, and he is such a turtle, I’m not sure it will get done in a timely manner. This is what will be for every room in this house; it may be quite an emotional job for him to go through every room and cupboard with a fine tooth comb. How do I navigate this without seeming insensitive? This is also the house that he raised his family and lived in with his ex-wife. I don’t know if this is relevant or not but thought I would throw that in.
Thanks so much for your insight!