Since this chorale prelude can be conveniently divided into 7 fragments according to chorale lines, it is best to practice it by playing one fragment at a time. The length of each fragment is determined by the fermata sign. As you practice each fragment, in the beginning play each of the three parts separately carefully observing that your fingering, pedaling, and articulation are correct. I have written an article previously about these points which you may read here. The left hand part will require more practice because it is written in a constantly moving broken chord texture. After you can play each of the parts with precision and accuracy at least three times in a row, practice combinations of two voices. Only after you master these combinations, play the entire fragment with all three parts. Try to resist the temptation to go to the next fragment before you master the previous one.
Practice at a tempo which allows you to play without mistakes. It could be very slow. However, as your performance gradually becomes better and better, try to play at the concert tempo which also should not be fast. The most important thing to remember about choosing the right tempo is this: pick such a tempo in which you can comfortably count all four beats in a measure and feel the alternation of strong and weak beats. Make larger breaks before the stronger beats which will allow you to emphasize the meter.
Although for practicing purposes this piece can easily be played using one manual, to perform it in public you will need two manuals with different sound colors. A gentle solo reed, such as the oboe (with or without the flute 8’) works well for the right hand part. Another option would be to play it on a cornet, or some other flute combination with mutations. Even a principal with a vocal quality may sound very good. A gentle tremulant might add to the expressive power of this composition. Play the accompanying parts using flutes with 16’ in the pedals.
If you want more information on registering your organ pieces, a great resource for organ registration practice in the Baroque period is "the Registration of Baroque Organ Music" by Barbara Owen, which I highly recommend.
If you practice “Ich ruf zu Dir, Herr Jesu Christ” according to my suggestion, you will gradually achieve the level when you can perform it with precision and clarity. For best results, make sure you play each chorale phrase at least three times correctly in a row. After each individual fragment can be played correctly, you can combine a couple of phrases at a time and make your fragments longer. Similarly to practicing other compositions by Bach, you must have the patience and inner motivation which leads to success. However, if you succeed in mastering this chorale prelude, it will be a perfect piece for your service playing or recital and your audience will love you for it. Therefore, it is well worth the effort.
You can get my practice guide on mastering "Ich ruf zu Dir" by Bach here. It comes with complete fingering, pedaling, articulation, registration, tempo suggestion, and detailed step-by-step practice plan which makes it perfect for study without an instructor.
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.