When it comes to studying Arabic for Islamic studies, speaking Arabic has a particular function in comparison to studying Arabic for business. If your goal in studying Arabic is to communicate face-to-face with native speakers at your job, it’s another story.
But most of us are studying Arabic to access Islamic texts and further our Islamic studies. For these learners, learning how to speak Arabic is something that may become more useful later on. Early on we want to master grammar and sarf and get fluent at reading, so we can pick up any text and read away. As our studies progress, learning how to speak Arabic on a basic level can be helpful in communicating with other scholars around the world, since Arabic is the modicum of Islamic communication throughout history. It’s the “universal language” of the scholars.
If you progress in your path to teaching higher-level studies like hadith, courses are often taught in Arabic as well. In that case you’ll be teaching in Arabic, perhaps all day.
Learning to listen to and understand Arabic is more pertinent than speaking, for the reason I just mentioned: higher-level studies may be taught entirely in Arabic, and you’ll need to listen and understand the teacher the entire period.
Composing Arabic in writing is also helpful to develop early on, as it deepens our understanding of nahw and sarf and helps us build our vocabulary.