Removing shoes (חליצת נעלים)
Even today in the Synagogue, the Priests Cohanim remove shoes before the priestly blessing, out of respect for holiness of the congregation assembled for prayer. (Talmud Sotah 40a)
The underlying idea seems to have been to bringing the dust of the street (which was connected with idolatry) into a place of prayer. The Jews of Arabia, following Sadducean custom, prayed like Priests, without shoes. As it says in the Haddith: Sunan Abu-Dawud Book 2, Number 0652: Narrated Aws ibn Thabit al-Ansari: The Apostle of Allah (pbuh) said: Act differently from the Jews, for they do not pray in their sandals or their shoes.