On Raqia, ask St. Louis SWORD OF FAITH and listen to how he used to have it, but broke it fighting a Roc in Zebul. In the Astral Sea, find the heavenly-blessed Roc. It hits pretty hard and has a ton of health, so bring a group or be a badass (whichever you're more comfortable with). When it's dead, take the shards of the Sword of Faith from it's corpse.
Find Sachiel at his forge on the first island in the Astral Sea and ask him SWORD OF FAITH, then give him the shards and he'll offer to reforge it if you get him some things. On that island are three crystals. Kill them all, and in the room with the third crystal, an empty crystal globe will spawn in a chest. Return to Raqia and go to the manna mill. Buy a pure silver I got for 21000 gold. North of Saint Louis, there's a column of divine light. RAISE GLOBE and your empty globe will be replaced by a half full one. RAISE GLOBE again and it will become a full globe. Return to Sachiel and give him the orb, and then the ingot, and enjoy your Sword of Faith.
This quest (and all the sword quests) are repeatable, so you can get yourself two if you're a rogue, and still be able to turn one in to Xapham.