Why the Second Tablets Carry Warnings
The differences between the two sets of Luchos show that after the golden calf, the Torah had to be given in a new way.
The Gemara asks why the first Luchos do not say "that it may be good for you" while the second do. The Lisa Rav answers that when the first Luchos were given, the evil inclination had left Klal Yisroel. They were like those who do exactly as they are told, with no need for threats or promised rewards. Once they made the calf, the yetzer hora returned, and the second Luchos therefore speak in a different voice. They add warnings, the words "as Hashem your God commanded you," and the reminder that they were slaves in Egypt. The phrase "as He commanded you" teaches that a mitzvah should be done because it is commanded, not for a benefit to come. Yet he stresses that both tellings are true, since the Torah said zachor and shamor in a single utterance.
Source: Nachalas Yaakov, Devarim (Vaeschanan, the two sets of Luchos)
Choose one thing you do regularly that is good, such as giving tzedakah, davening or helping a neighbour. Ask yourself honestly what is driving it: habit, a wish to be seen, or a hope of reward. You need not stop doing it while you check. Then, once today, do it with one plain thought in mind, that Hashem asked for this and you are glad to answer. A deed done in that frame tends to hold steady when the benefits are slow to appear.