Shabbos 153b: One may cover up Halachos l'Shem Shamayim. E.g. if one was on the road when Shabbos was about to come, Chachamim taught ways to bring his wallet to a safe place, but did not teach one of them (to carry less than four Amos at a time, lest one accidentally carry four Amos at once in Reshus ha'Rabim.)

Rashi: Matters such as Ma'ase Merkavah and Ma'ase Bereishis should be covert.

Malbim: In Divine matters, honor is hiding and covering. Intellect understands only matters within time and place, but not matters above human understanding. Whatever one says about them is merely a Mashal and garment [for the Emes]. The inside is hidden. This is why we do not expound Ma'ase Bereishis and Ma'ase Merkavah. Chachamim clothe the matters and hide them in riddles and hints.

Shabbos 153b: One should not cover up things due to a person's honor or wealth.

Rashi: When you seek the honor of kings or of Chachamim, who made fences for Torah and decrees, you should investigate and ask the reason. However, when you investigate Ma'ase Merkavah, Ma'ase Bereishis and Chukim written in the Torah, e.g. Mitzvos that the Satan challenges, like [why the Torah forbids] eating pork, Kil'ai ha'Kerem and Sha'atnez, do not investigate. Rather, cover the matter, and say that it is the King's decree.

Malbim: In matters of the king's conduct, it is honorable to investigate and not hide. Their conduct is based on etiquette, and senses perceive it. It is good to publicize their good conduct; hiding shows that their conduct is not straight, therefore they hide it.