This psalm was written as a love song with a composite picture in mind of a Jewish king and his bride. It is considered a Messianic psalm because parts of it are quoted in Hebrews 1:8-9 in reference to Jesus Christ (Messiah).
The imagery and wording speak of a king who is immortal. It looks ahead to the long-awaited Jewish Messiah establishing His kingdom on earth. A kingdom noted for its eternal permanence, favor, and justice.
Today, social justice is a hot topic, but clamoring for justice is nothing new. Protests, even revolutions, are undertaken for the cause of justice. But true justice isn't a legal issue, it's a moral one.