Many writers run out of steam by the time they get to the end of a long writing session. They are tempted to skimp not only on editing but also on the conclusion. Too many writers simply rewrite the thesis or the whole opening paragraph, add the topic sentences from some of the key body paragraphs, and let the essay trail off. That is better than nothing, because a central function of the conclusion is to sum up the points of the essay.
Slightly better is to add a sentence or two to suggest something new for the reader: an implication to follow up, an idea for further research, a challenge that must still be met, a recommendation for further reading, and so on. This material can be extended into an entire paragraph or two when the essay is long enough.
In several fields, the concluding section is expected to take a certain form that does much more than sum up the essay. In social science fields, for example, an essay that presents your research results often should include a section on the limitations of the research (such as ways that the research method could be improved, or cautions about the applicability of the research). It is important to learn what standards apply to essays in your field.