Visuddhimagga XIV-141

465. Saranti tāya, sayaṃ vā sarati saraṇamattameva vā esāti sati. Sā apilāpanalakkhaṇā, asammosarasā, ārakkhapaccupaṭṭhānā, visayābhimukhabhāvapaccupaṭṭhānā vā, thirasaññāpadaṭṭhānā, kāyādisatipaṭṭhānapadaṭṭhānā vā. Ārammaṇe daḷhapatiṭṭhitattā pana esikā viya, cakkhudvārādirakkhaṇato dovāriko viya ca daṭṭhabbā.

（10）依此而（相应诸法）忆念故，或他自己忆念故，或只是忆念故为「念」。它有不使流去的特相。有不忘失的作用。以守护或向境的状态为现状。以坚固之想或身等念处为近因。当知念能坚住于所缘故为门柱，因为看护眼门等故如门卫。

Ñ(XIV,141): (x) By its means they remember (saranti), or it itself remembers, or it is just mere remembering (saraṇa), thus it is mindfulness (sati). It has the characteristic of not wobbling. Its function is not to forget. It is manifested as guarding, or it is manifested as the state of confronting an objective field. Its proximate cause is strong perception, or its proximate cause is the foundations of mindfulness concerned with the body, and so on (see M. Sutta 10). It should be regarded, however, as like a pillar because it is firmly founded, or as like a door-keeper because it guards the eye-door, and so on.