From the ESV Online Study Bible:
Clearly the return of God’s glory to the temple is one of the most dramatic moments in the book. His return here is the restoration counterpart to the departure in 10:18–22 and 11:23. It also brings completion to the temple tour: all that was lacking from this sacred space was God. However, this moment also forms a new beginning. The arrival of God’s glory in his temple inaugurates a new era in the relationship of God and people, and this becomes the focus of the remainder of the vision.
Knowing God through His Word ... Day by Day 