Rabbinic Does Not Mean Optional
The Raavad answers those who set aside the laws of stains because they are rabbinic, and shows that the Sages made them to strengthen the Torah.
In Baalei HaNefesh the Raavad meets an argument that the laws of stains no longer apply today. Their defenders say that stains are only rabbinic and matter only for questions of purity. He calls this empty, and he answers from the Gemara itself. The Sages, he points out, said that stains were not enacted to ease the Torah's laws but to make them stricter, as a fence around the Torah, and so they concern the prohibition itself and not only purity. He adds that the Gemara speaks of stains that could lead to a woman bringing a korbon, which would make no sense if they mattered only for purity. For the Raavad, a rabbinic fence is a living part of the Torah, built to protect it.
Source: Baalei HaNefesh, Shaar HaKetamim, siman 1, paragraph 2
It is easy to say that something is only a custom or a rabbinic rule and set it aside. The Raavad reminds us that such rules were built to guard what is precious. Today, take one practice you have been casual about, such as washing before bread, a bracha before eating, or a minute of quiet before davening, and keep it with full attention. Ask what it protects, and let that understanding make it meaningful.