The mysteries of Regaleira

Via Divagar sobre tudo um pouco a beautiful blog by Maria(...) Paragem obrigatória na Capela da Santissima Trindade, nela estão representados Santa Teresa d'Ávila e Santo António. No meio, a encimar a entrada está representado o Mistério da Anunciação - o anjo Gabriel desce à terra para dizer a Maria que ela vai ter um filho do Senhor - e Deus Pai entronizado. Na Capela econtra-se a imagem do Delta-radiante (ou Delta-Teúrgico), com o olho de Deus sobreposto à cruz templária, emblema maçónico do Grande Olho Arquitecto do Universo.(...) 
It says basically the following: it is compulsory to stop (in the visit) in the Chapel of the Holy Trinity where the Saints Teresa d''Avila and António are figured. In the center (of the Chapel) over the entrance a Saint Gabriel descends to Earth to announce that Mary will have a son of the Lord, the Father. In the Chapel an image of the radiant Delta is visible with an All-Seing Eye over a Templar Cross, the symbolic figuration of the Grand Architect of the Universe (...)

ALL-SEEING EYE

An important symbol of the Supreme Being, borrowed by the Freemasons from the nations of antiquity. Both the Hebrews and the Egyptians appear to have derived its use from the natural inclination of figurative minds to select an organ as the symbol of the function which it is intended peculiarly to discharge. Thus, the foot was often adopted as the symbol of swiftness, the arm of strength, and the hand of fidelity.
On the same principle, the open eye was selected as the symbol of watchfulness, and the eye of God as the symbol of Divine watchfulness and care of the universe. The use of the symbol in this sense is repeatedly to be found in the Hebrew writers. Thus, the Psalmist says, Psalm xxxiv, 15: "The eyes of the Lord are upon the righteous, and his ears are open unto their cry," which explains a subsequent passage (Psalm cxxi, 4), in which it is said: "Behold, he that keepeth Israel shall neither slumber nor sleep.
In the Apocryphal Book of the Conversation of God with Moses on Mount Sinai, translated by the Rev. W. Cureton from an Arabic manuscript of the fifteenth century, and published by the Philobiblon Society of London, the idea of the eternal watchfulness of God is thus beautifully allegorized:
"Then Moses said to the Lord, O Lord, dost thou sleep or not? The Lord said unto Moses, I never sleep: but take a cup and fill it with water. Then Moses took a cup and filled it with water, as the Lord commanded him. Then the Lord cast into the heart of Moses the breath of slumber; so he slept, and the cup fell from his hand, and the water which was therein was spilled. Then Moses awoke from his sleep. Then said God to Moses, I declare by my power, and by my glory, that if I were to withdraw my providence from the heavens and the earth, for no longer a space of time than thou hast slept, they would at once fall to ruin and confusion, like as the cup fell from thy hand."
On the same principle, the Egyptians represented Osiris, their chief deity, by the symbol of an open eye, and placed this hieroglyphic of him in all their temples. His symbolic name, on the monuments, was represented by the eye accompanying a throne, to which was sometimes added an abbreviated figure of the god, and sometimes what has been called a hatchet, but which may as correctly be supposed to be a representation of a square.
The All-Seeing Eye may then be considered as a symbol of God manifested in his omnipresence-his guardian and preserving character-to which Solomon alludes in the Book of Proverbs (xv, 3), where he says: "The eyes of the Lord are in every place, beholding (or, as in the Revised Version, keeping watch upon) the evil and the good." It is a symbol of the Omnipresent Deity.
MacKey Revised Encyclopedia, Volume 1, Albert G. Mackey. New York : Macoy Publishing and Masonic Supply Co., Inc., 1966. pp. 52-53