To make thine enemies thy footstool", as in Psalm 110:1, signifies to subjugate and keep under the hells. Here a footstool signifies the lowest region under the heavens -- that is to say, the hells. A footstool, as in Psalm 132:7, signifies the Lord's church in the earths.

(Odkazy: Apocalypse Explained 607)

284. "And we shall reign on the earth." This symbolically means, and they will dwell in His kingdom, He in them and they in Him.

To reign on the earth means nothing other than to be in the Lord's kingdom and to be united with Him in it, according to these words of the Lord:

...that all (those who believe in Me) may be one; (and one) as You, Father, are in Me, and I in You, that they also may be one in Us... The glory which You gave Me I have given to them, that they may be one as We are one, I in them, and You in Me..., that they also... may be with Me where I am... (John 17:20-24)

So then, since they are thus one with the Lord, and together with the Lord form the kingdom that is called the kingdom of God, it is apparent that nothing else is symbolically meant by reigning.

Reigning is mentioned because of the prior statement, "You have made us kings and priests;" and because kings symbolize people who are governed by wisdom springing from Divine truths from the Lord, and priests symbolize people who are governed by love springing from Divine good from Him (no. 20).

It is because of this that the Lord's kingdom is also called a kingdom of saints (Daniel 7:18, 27); and of the Apostles it is said that with the Lord they will judge the twelve tribes of Israel (Matthew 19:28), even though it is the Lord alone who judges and reigns. For He judges and reigns from Divine good by means of Divine truth, which they have in them as well from Him. But anyone who believes that what they have from the Lord is something of their own, is expelled from the kingdom, that is, from heaven.

Reigning has the same symbolic meaning in the following places in the book of Revelation:

...they shall be priests of God and of Christ, and shall reign with Him a thousand years. (Revelation 20:6, cf. 20:4)

And of those who will come into the New Jerusalem, it is said:

(The Lamb) gives them light. And they shall reign forever and ever. (Revelation 22:5 [cf. Revelation 21:23])