The word here translated "Vicegerency" is, in the original Arabic, "viláyat", which has a range of meanings including "vicegerency", "guardianship", "protectorship" and "successorship". It is used in relation to God Himself, to His Manifestation, or to those who are the appointed Successors of a Manifestation.
In this verse of the Aqdas, Bahá'u'lláh warns against allowing such concepts to blind one to the "sovereignty" of the new Divine Manifestation, the true "Vicegerent of God".