“All economists share the error of examining surplus-value not as such, in its pure form, but in the particular forms of profit and rent. What theoretical errors must necessarily arise from this will be shown […] in the analysis of the greatly changed form which surplus-value assumes as profit.”

— Marx’s opening statement to “Volume 4” of Capital, Theories of Surplus Value

There is a difference between profit and surplus-value. It can be summed up pretty much as follows:

1. Surplus value is the general, abstract form of economic exploitation which enables a non-working ruling class. Profit is one concrete form taken by surplus-value.
2. Profit includes constant capital. Surplus value does not.