The `both` in this verse is us and His HolySpirit.
The `middle wall of partition` in this verse is the veil of the temple Exo 26:33 Mat 27:51 representing sin that separated us from the HolySpirit.
We are AcceptedInTheBeloved Eph 1:6.
Christ Jesus has made it possible for us to enter the HolyOfHolies - the very bosom of His HolySpirit Eph 2:14.
And not only that, He has made it possible for the HolySpirit Himself to dwell in us through SpiritBaptism Joh 14:17.
We are one with the HolySpirit through the finished work of Jesus Christ Joh 17:21.