TRVPHOUR

So, I'm working on amod, and currently learning forge and Minecraft mod development and I've run into a problem. I've developed the mod and would like to test it so I press the green arrow button on IntelliJ which runs the Minecraft Client, which it did. My Minecraft loaded up and all just fine no problems, however my mod didn't load. I've been trying to figure it out for the longest, even going over the forge documentation again and running setupDecompWorkspace again as well as genIntellijRuns. Nothing. I then found something on a forum and ran gradlew runClient, which rain Minecraft and loaded my mod as needed. My question is what is causing this, or what exactly runs my src file and compiles it for Minecraft, so that I know what to look for or maybe a mistake I made. Thanks.