What was the philosophical message of ancient Epicureans?

In Horace, the phrase is part of the longer carpe diem, quam minimum credula postero, which can be translated as "Seize the day, put very little trust in tomorrow". The ode says that the future is unforeseen and that one should not leave to chance future happenings, but rather one should do all one can today to make one's future better. This phrase is usually understood against Horace's Epicurean background.