Revelation (8b-10): God's lavish grace is further seen in the revelation of His cosmic will to His people. This is His cosmic will in that it encompasses "all things," both "in the heavens" and "on the earth." Now, the will of God (hidden before, but now revealed to us) is this: to sum up all things under the heading of Jesus "the Christ." At a very exact time, at "the fullness of times," God will execute His plan to bring all things under Jesus as the thesis, the main point for the existence of everything. Everything will find its ultimate purpose in Christ! For us who love the Lord, this is truly God's "kind intention," for there is no better person for whom the universe should exist than our dear Savior.
Possession & Pledge (11-14): We belong to God (1:11)! We are God's "own possession" (1:14). And our purpose as God's own people is this: to be “to the praise of His glory." We are to praise Him and give voice to His great worth (1 Pet. 2:9). This sublime cause is what God predestined us for! And He has the power to bring it all to pass, for He "works all things after the counsel of His will." All of God's own will indeed praise Him. Lastly, we have the promised Holy Spirit, who is in us as God's pledge of our future redemption. The Spirit ever sanctifies us till we're glorified. We are made holy, for He dwells in us!
 1:8 continues the sentence on God's grace: "which He lavished on us, in all wisdom… making known…"
 "Mystery" means something concealed/unknown. The person and the time of Christ was unknown (1 Pet. 1:10-11), and God has revealed to us that Jesus Christ is the person under whom all things will be ordered.
 "Summing up… in the Christ [articular in Greek]" points to Jesus "the Christ" as the thesis/heading. In the original, "summing up" contains the idea of a head. Jesus is repeatedly the head in this book: 1:22; 4:15; 5:23.
 "Administration" is stewardship/management or the activity/execution of it. The latter is the sense here. "to put into effect" of NIV well captures this meaning. This is the carrying out of God's plan at the right time.
 "We have obtained an inheritance" is better rendered "we were obtained [the verb is passive in Greek] as an inheritance," per NASB's footnote. God also speaks of Israel similarly: Ex. 19:5; 34:9; Deut. 9:29; 32:9.
 The Spirit was promised to come, hence, He is "the Spirit of promise." Cf. Luke 24:49; Acts 1:4-8; 2:38-39.