This is an incredible album. It's amazing in its abundance of pure, sacred sound energy, as are all of Ayler's recordings, especially with this group. This is stream-of-consciousness, meditative music (although it is in no way calming or relaxing). If you are into that kind of thing, then look no further.
If you're familiar with Ayler, then you know what this record sounds like (and you've probably even heard it). If you aren't familiar with him, then there's no point in trying to describe the music; it's meant to be experienced, not talked about. Murray lays down a free pulse, or rather a stream, on top of which dances Peacock's fluttering bass and Ayler's screaming abandon. To many it may sound like a meaningless free-for-all, but if you listen closer it becomes a conversation. It has been said that Ayler practiced playing scales so fast that he could do them in fast slurs and make it sound like one sound (the Holy Ghost box set for more on this). He swoops from above the high register down as low as he can; you've never heard such a strange tone as his. And during all this "madness," you must be thinking "What does it all mean?" Albert Ayler himself always used to say "You think it means something? Why does it have to be about something? It doesn't mean anything; it just is!" (Again, see the Holy Ghost box set). If you can get inside of it, then you will. If you can't, then you won't. It's as simple as that.
Spiritual Unity is considered Ayler's masterpiece, although it is no different (or better, in my opinion) than the rest of his work from 1964. It's just a very clear look into what he was doing at that time.
A point of interest is how early this recording is in relation to a lot of other free-jazz (July 1964). There was a huge underground free jazz thing happening at that time, but a lot of people weren't aware of it.
I think that this was Ayler's best group. Although it was fairly short lived, it is easily the most influential of the many Ayler lineups. Gary Peacock was very young at the time, I believe only 19 or 20. He was one of a handful of bass players who were using the "new" bass technique, which was to play with all four fingers instead of the usual one or two. This is probably most well-known by those familiar with Scott LaFaro, as he was one of the first to use it. However, most of the free-jazz bass players had studied it, too: Cecil McBee, Richard Davis, Art Davis, Henry Grimes, Peacock, and others. I think Ron Carter may have used this technique as well.
Sunny Murray was a very significant figure at the time as well. He was the first "free" drummer; that is, the first drummer to play regardless of time constraints. Although all the other avant-garde drummers caught on to this very quickly, Murray was for sure the first. Other notable drummers who played in this style are Rashied Ali (probably the greatest), Beaver Harris, Andrew Cyrille, Ronald Shannon Jackson, and Milford Graves, most of whom played with Ayler at some point.
Ayler's music changed a lot in 1965 and especially 1966. I love all the 1964 recordings because they are wild and free, while still possessing a certain casualness that makes you want to listen to them over and over again. It's sort of like he's saying "Yeah, I'm doing this! Why don't you get with it?" This is amazing stuff!