Your guild level is determined by taking the average (rounded to the closest integer) of your 14 primary skills. Only the real, useful skills at the end of the tree, like fa.ri.de.se or fa.po, NOT fa.ri.of. In other words, you'll gain a GL every 14 levels in a skill. It is a common misunderstanding that your level in Faith is related to your GL. Let me explain the difference: your level in Faith is determined by your levels in fa.ri.de, fa.ri.mi, fa.ri.of and fa.po. Hence, fa.po has much more impact on your Faith level than any other subskill. This causes the difference between your GL and your Faith level.