Marx rejected Hegel's Idealism, his belief that Absolute Spirit or Mind is reality.
Sensible reality is primary.
Just as religion was a form of alienation for human beings, so was German philosophy because it divorces man from reality, making him only a spectator of processes in which he was involved. Initially everything is Nature, including human beings. This differentiation cannot take place in thought however, but only in objective reality. Man overcomes alienation, negates the negation. The products of ones labor belong to the laborer.