This verse describes Christ, not only as the once-for-all perfect sacrifice for sin but also as the high priest who is uniquely qualified to offer His sacrifice to God. Because He was conceived by the Holy Spirit, He was undefiled by the sin of Adam, and because of His personal holiness during His earthly life, He didn’t have to purify Himself before entering the holy of holies.
Under the Law, the high priests had to repeatedly offer sacrifices for their own sin as well as for that of the people. Because He was holy by nature, Christ was particularly suited or “fitted” to be our high priest, not in the earthly temple, but in the very presence of God.
Other names and characteristics of God that begin with U are:
Thanks be unto God for his unspeakable gift. 2 Corinthians 9:15
Although I have no Scriptures for these descriptions, some other adjectives that can be applied to God are unique, understanding, unwavering, unexplainable, unfathomable, and unchangeable.