Colossians 1:19

God’s fullness would dwell in his son, this verse states. This is after a verse that speaks about Christ coming to be first in all things. This verse takes it further, revealing God's reasoning for bringing forth the Jesus into the world and having Him die and rise from the dead. It was so that all God's fullness would dwell in the Son.

Where was the fullness before?

That God wants all his fullness in the Son means that fullness was elsewhere. Remember, Jesus is God, and God does not need any improvement. Understand that. However, when God in Christ created principalities and powers, He endowed them with some authority and power. That was His choice.

In Adam, Angels

If humanity had no authority, they would not be capable of rebelling. In other words, humans would not rebel unless they could use that authority apart from and in disobedience to God. As an example, Jude lists angels who left their place of authority (Jude 1:6).

When God made Adam, He conferred some authority upon him. Now, with the incarnation, death, and resurrection, the cosmic power was fully shifted to one man, Jesus Christ. Not to Adam or any other being, but to Christ. That fullness dwells in Him. He said all authority and power have been given to Him (Matthew 28:18-19), through victory over death.

Some of God's fullness was in the angels and also in Adam, but now everything is in Christ. All of God's fullness would dwells in Christ.

But, the end is near for other rules

To start from the beginning, we see that there are thrones, dominions, principalities, and even humanity in rebellion, that seem to have a will of their own and conduct things in their own way. That will soon come to an end.

God has apportioned authority in different domains, including thrones and dominion, on earth and among heavenly beings. In the age to come, the rulers will be Christ and His followers (John 5:22, 1 Corinthians 6:3, 2Timothy 2:12, Revelation 20:6, Revelation 5:10, Revelation 22:5, Revelation 11:15). Christ is the head of all principalities and powers now. And also the head of the church. All fullness truly dwells in him.

Regarding Jesus, the Bible says He was made, for a little while, lower than the angels, so that by God's grace, He would experience death on behalf of everyone (Hebrews 2:9, 14), meaning He was made mortal. The result, after He rose from the dead? And He was crowned with glory and honor after his victory over grave.

Daniel puts it this way: "To Him was given ruling authority, honor, and sovereignty" (Daniel 7:14a).

Conclusion

There can never be a rebellion like what happened with the devil, with man, or with the angel that rebelled against God ever again. The cosmos is restored and cannot fall into ruin again, because all of God's fullness now dwells in one man, Jesus, who is also God.