It is the perennial problem and issue of every worship leader and/or choir director. If they are properly trained then they are fully aware of the need to train their singers as opposed to only rehearsing them.
The primary concern is one of time. Sunday is coming and your group will be on display for everyone to hear and the pressure is to make sure that they are ready. But the problem with continual rehearsing is that problems perpetuate and the growth is slow and tedious. It is the duty of every choir director to vocally train their amateur singers for proper vocal health and ear-training. Over time the director will realize that the level of music able to be achieved is limited and a ceiling will be reached in their musical acquisition.
Training, does take away from the time to rehearse but the pay-offs are worth the effort. When training a choir there are a number of things that must be done and I'm not going to set a certain order but will give advice to what needs to be done. The order is determined by the needs of the group.
Breathing: The proper technique of breathing is fundamental, foundational, and paramount.
Good Vocal Production: Once breathing correctly has been established it is essential that the director work on proper spacing inside the mouth and on the quality of vocal production. Amateur singers will resort to spread vowels and belting very quickly and this will hinder your group from proper tuning.
Ear-training and Intonation: This step is critical for every singer and musician. The ability to hear where their part sits in the orchestration and its relationship to others is very important. Establishing tuning points within songs for the choir to check their intonation during live performances is a valuable tool for them use as guide posts. Ear-training and Intonation are very similar but not synonymous but I will include them into the same category due to issues of space.
Health and Rehearsal Techniques: Proper eating, sleeping, and drinking habits are the bedrock of healthy vocal production. Along with the directors recognition of when the group needs to "sing out" as opposed to "mark singing". Mark singing is a valuable tool to save the voices during long rehearsals and extended periods of singing. It is very possible and easy for choristers to learn their music and listen for intonation while mark singing while at the same time saving their voices for the moments when full singing is required.
There are many more areas of vocal techniques such as vowel modifications and warm-ups that any director should be aware and well versed in how to properly apply them. So, the road to a great choir is built step by step with an
intricate plan on how to get them to a place of excellence but the idea of continually rehearsing will hinder that progress and leave the director with frustration.