R. Yonah #1: After warning to seek Chachmah, this Parashah warns about serving the Creator. From Chachmah one comes to Avodah (refer to 1:7:1:2). This verse warns to guard Chachmah after learning it, and not forget it.

R. Yonah #2, (4:20): Do not forget My Torah, to fulfill it in practice. The Torah warns us against Peshi'ah in Mitzvos - "Hishamer Lecha u'Shmor Nafshecha Me'od Pen Tishkach Es ha'Devarim

Malbim: Mitzvos must be done in practice, or to refrain from Lavim. Most oppose the heart's desire. The heart is the power of authority in the Nefesh. It rules over powers of the Nefesh, to direct their actions according to Hashem's Mitzvos.