The goal to learn new music as opposed to sight-read them is wonderful. In fact, the two are strongly connected.
You see, if your primary goal is to play in church, then this might well be your motivation behind learning new music for services. You don't need to play everything new every Sunday since this will be a very great burden. You want to enjoy music and not to feel like you have to prepare something new in a short amount of time.
Usually there are 4 places for organ music in the worship service of various denominations today (prelude, offertory, communion, and postlude). One possibility for you would be to learn one new short work each week or every two weeks and repeat others from your current repertoire. This piece does not have to be long nor too complicated. In fact, a chorale prelude of 1-2 pages is an optimum duration for liturgical organ playing.
If you like sight-reading, this does not necessarily mean you should stop practicing it. In fact, this is a tremendous tool in any organist's arsenal of skills. Many people would like to get better at sight-reading, so if you already have reasonable skills, you have an advantage. An ability to play unfamiliar music at sight makes a process of learning new pieces much easier.
If you really want to develop unbeatable sight-reading skills, check out my systematic Organ Sight-Reading Master Course. To complete the practice material of this course will only take 15 minutes a day of practice but you will learn to sight-read any piece of organ music effortlessly.
I often suggest organists two practice both sight-reading and learning new material regularly. This ensures that both skills are being developed at the same time.
The ultimate goal would be to be able to play the music that you love at sight fluently, without interruptions, and mistakes. However, you are probably thinking that nobody can achieve this level.
There is a story about Bach, who was a great sight-reader and usually could play anything written on the music sheet. But one day during his visit with his friend he made a mistake on the harpsichord by trying to play the same spot three times in a row and said: "No, it is not possible to sight-read everything".
So the take-away message for you would be to take a piece of your choice and practice it on a deeper level for church service. For best results work in separate voices and voice combinations. Practice in short fragments to avoid mistakes.
By the way, do you want to learn to play the King of Instruments - the pipe
organ? If so, download my FREE video guide: "How to Master Any Organ Composition" in which I will show you my EXACT steps, techniques, and methods that I use to practice, learn and master any piece of organ music.