This is a piece of Hegelianism. Marx was very impressed by Hegel while in college, and in his 20s was a leader of a group called the Young Hegelians, who were left wing. The mainstream Hegelians were conservative. He stayed a sort of HGegelian -- this is controversial, but I believe it to be true -- his whole life. Anyway, one thing that Hegel tried to do was to overcome subjective/objective divisions, which he regarded as as symptomatic of alienation, and part of this involved complicated arguments that moral standards are both objective, in the sense that they are true and the same for all, and subjective, in the sense that they are self-imposed constraints that we do come, or can come under the right circumstances, to freely adopt for ourselves. This is very difficult stuff, so if it is not immediately transparent, it's not that you are dumb, it's that it's hard to explain.
jks
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