Musar על יומא 77:3

[see Chapter II on Vayikra 11:43]

The Torah (19,26-29) continues with legislation not to imitate the "cultural" standards of the Gentile nations. All their so-called culture is based on idol worship, a form of being ערל לב, of uncircumcised heart. When a human being initiates the process of defiling himself, other forces will defile him even more (Yuma 39). This is why the process of rehabilitation has to begin immediately, before one becomes progressively more defiled, more impure. We can interpret the Torah's demand מפני שיבה תקום "arise in the presence of an aged person" (19,32) as a warning not to wait until one's evil urge has become so old that it does not tempt one anymore. Compare the comment of the Zohar on this verse (Sullam edition page 45). The word מפני then is read as לפני.