The subject of this verse and therefore the speaker is the same one who has spoken to us by the Son, who has not addressed the angels as ‘Son’ or declared himself to be their Father, who has brought the first begotten into the world and commanded the angels to worship him. It is God the Father, identified in verse 1.
The Son’s kingdom is characterized by righteousness, integrity, uprightness. How different to the kingdoms of this world. This is its unvarying characteristic. It has a scepter, the symbol of kingly power, which is righteous through and through, which ensures that only righteous acts are carried out in the name of the King, and since this is an absolute monarchy, ruled by the King who sees all that takes place in his realm, then nothing is carried out in this kingdom without the word and approval of the King. And our security rests on that. What absolute security in the eternal heavens! You will never turn a corner, round a corner, and discover something evil, something contradictory, something polluted, something disappointing, something horrible or shocking. It's purged of everything like that.
How wonderful to be a member of this kingdom! We should above all else long to know, and strive to know, the entrance qualifications to his kingdom. How glorious to have such a King over us, ruling according to his perfect law, and imposing his perfect justice on all his citizens. We enter this kingdom by the new birth, and therefore every citizen is also a member of God’s family. How we long for an end to fallen human authorities and kingdoms, and for them to be eternally replaced by the kingdom of God’s Son.
The Jewish teachers of old were teaching something quite different: that this was a psalm which was designed to congratulate Solomon on his marriage, or his first marriage. But of course the psalm in no way fits Solomon when you read through. It’s a psalm, which refers to God, and one who is obviously incarnate God. He is called the King, the Mighty One and in verse 6 of the psalm he is called God. The Hebrew word though plural, as always when used of God, is spoken to a single individual. Though used on rare occasions of angels in the plural, it is never used of an individual angel. It is used in Hebrew in the vocative, as nearly all translations agree, although there is no specific form for the vocative in the language. It is also vocative in Greek, even though a nominative form is used. It cannot be the subject of the implied verb ‘to be’ since a subject has already been provided: ‘Your throne’. The one spoken to is therefore Elohim, God himself, and here we have the Father addressing the Son as God.