The antecedent of "him" is Christ. This is apparent from the context of the next three verses and is also revealed in DC 113:1-2. This passage is similar to another Messianic passage of Isaiah, 'The Spirit of the Lord God is upon me' (Isa 61:1).
As with other Messianic passages, verses 2-5 do not find their complete fulfillment until the Second Coming and the Millennium, for that is when He will come to destroy the wicked and establish His righteousness.