Assuming that you are writing about the Jake Reinvented Project and drawing parallels between it and F. Scott Fitzgerald's The Great Gatsby, your thesis should have points of comparisons and contrasts between the two main characters which you have illustrated in the body of your essay. So, now to write a conclusion should pose no great challenge as a concluding paragraph is essentially a restatement of the thesis with a summation of these main points followed by a "clincher," or thought that springs from what has been written.
For example, if you have written that Jake and Jay Gatsby are similar in their ________and __________, but unlike in ___________, you can summarize these points by beginning your conclusion something like this:
With the desire to recapture the past and alter it, both Jay Gatsby and Jake _______________________________; however, they _________________. Because of these parallels between the two characters, ______(here restate your thesis). Clearly, they are two men with dreams that have dissolved into illusion.