when obedience becomes our goal, it is no longer an irritation; instead of a stumbling block, it becomes a building block"

i think this quotes means that when you have a goal then there are certain things that you have to do in order to achieve your goal that you have. your goal keeps building up all the time so that every time you meet it you can go higher. make a different goal every time you meet the last one. your goals build up at the end so that it can help you accomplish the big goal. your goal keeps adding up so that you can go higher than where you are already.