You can’t start a fire with big things. You use little things and shelter it. Take care of it or it will extinguish. Once the fire has established it no longer needs shelter and is strong. This is akin to faith. Faith is weak to begin with but will become strong. The community protects this fire from the winds (tests). So the mosque is important for lectures/lessons/activities/dhikr/etc. (Paraphrased from Shaykh Faraz Rabbani)