Head up to the Skyforge to find all of the Companions gathered around in honor of Kodlak Whitemane. Afterwards, Eorlund Gray-Mane asks you for the fragments of Wuuthrad and informs you of a final piece that can be located in Kodlak’s room in the Living Quarters of Jorrvaskr. Head to Kodlak’s room which is to the East of the table which he usually sat. Check his bedside end-table for the final fragment and his journal which details the way Kodlak truly felt about you.
Return to Eorlund with the final fragment, and head to the underforge to meet with the other Companions to learn that Vilkas knew why Kodlak sent you to slay the Glenmoril Witch. Although Aela disagrees, she understands and agrees to help the others fulfill Kodlak’s wishes. Vilkas informs you of a way to help Kodlak and tells of Ysgramor’s Tomb which can only be entered using Ysgramor’s blade: Wuuthrad, which lay in pieces. Enter Eorlund, with a repaired Wuuthrad in hand, who hands Ysgramor’s weapon/key to you.
Follow the Companions (or fast travel to save hassle) to Ysgramor’s Tomb where the Companions are inspecting the weaponless statue of Ysgramor. Place the Wuuthrad into the statue’s hands to open a passage leading into the tomb. Travel with your Companion brethren into the tomb dispatching ghosts of Companions past making sure not to wander too far from your shield-siblings.
Continue to dive deeper into the tomb killing spiders, slashing cobweb walls, and killing ghosts until you reach a room with a handle at the east end. Activate the handle to open the gate along the Northern wall in order to gain access to the Flame of the Harbinger. Speak with the old friend found behind the Flame to learn of its purpose, activate the Flame using one of the witch heads and help your old friend battle the new foe in the cleansing ritual.
After the foe has been slain, speak with your old friend again to complete the quest. Head up the wooden ramp in the NorthEast corner of the room; pull the chain on the Eastern wall to open the gate leading to the spiral staircase. Climb up the stairs and activate the chain that you eventually come across to open the stone wall leading back to the Ysgramor statue. Note: you may now return to Jorrvaskr at anytime to complete more subquests however, there is a word of power just minutes away.
Continue to head West to the exit on the West wall; once outside follow the steps up the mountain to the East to reach the new Word of Power.