How can the death of a creature shake the Throne of the Most Merciful, which represents the Majesty and absolute Power of God, is this not a blemish upon the Exalted Self?

The shaking of the Throne at the death of Sa'd ibn Mu'adh is a mutawatir (mass-transmitted) hadith. Hadiths concerning the Attributes (of Allah) and related matters of the Unseen must be accepted as they have been reported, without interpretation or anthropomorphic description. Just as we believe in the Most Gracious's (Allah's) ascending over the Throne, we also believe in the shaking of the Throne at the death of Sa'd ibn Mu'adh, whether that was out of joy from the Throne itself or from the Lord's joy at meeting His servant. This shaking does not diminish the grandeur of the Great Lord; rather, it pertains to the attribute of the created Throne.