But of the Son he says, “Your throne, O God, is forever and ever, the scepter of uprightness is the scepter of your kingdom. You have loved righteousness and hated wickedness; therefore God, your God, has anointed you with the oil of gladness beyond your companions.”
There are two possible readings of ‘God’ in verse eight. Either in the vocative (‘your throne, O God …’) or as the subject (‘God is your throne …’). So this verse may not be addressing Jesus as God at all. It is also worth remembering that Hebrews 1:8-9 is quoting a psalm (Psalm 45), which was first applied to a human king. If the psalmist thought it appropriate to call a man ‘god’ then would it not also be appropriate for Jesus to be called ‘god’ in this context.
It is also worth bearing in mind that the terms ‘therefore’ and ‘anointed’ in this passage imply subordination. The psalmist is saying that the king, and later Jesus, “love righteous and hated wickedness” and it was for this reason (hence “therefore”) that God gave him a new status. If Jesus was God he would be de jure entitled to the throne and sceptre by his very nature. The psalmist is saying that these things were given to Jesus by God.