Что такое cetana?

What is volition (cetana) [intention]? It is construction by the mind (chittābhisaṃskāra), mental activity (manaskarma). Its function is to direct the mind in the domain of wholesome (kuśala), unwholesome (akuśala) or neutral (avyākṛta) actions.

What is action dominated by the defilements (kleśādhipateyakarma)?
1) The action of volition (cetanākarma) and
2) the action carried out after having willed it (cetayitvā karma).168

23) What is an arhat of voluntary nature (cetanādharma arhan)?
It is a person who, having weak faculties by nature, distracted or not, falls from his state of bliss in this life if he is non-reflective, but does not fall if he is reflective.459

9.3.4.1.2. Volition (cetanä) — That which causes the mind to be karmically creative (citta-abhisamskära). It is the mental karma. The Avatära28 describes it thus: "It moves forth (pra-Vsyand) the thought." Samghabhadra's definition29 runs: "cetanä is that which causes citta to do kusala, akusala and avyäkrta [karma], resulting in good, bad and neutral [vipäka]. On account of the existence of cetanä, the citta has the activity of moving forth with regard to the object. It is like a magnet, owing to the force of which iron can move forth."

Dharmaträta states that "the citta-caitta-s are [but] the specific modes of cetanä (cetanä-visesa)".18 This means that whatever one may choose to call it — citta or caitta — the mind arises specifically; mental activity as such being characterized by cetanä — 'consciousness', 'understanding'. As a matter of fact, citta (> caitta), cetas (> caitasika) and cetanä are all derived from the same root √сit, and cetanä, in a more general sense (than that of 'volition'), can mean 'understanding', 'consciousness', etc., thus referring to mental activity in a general sense.

The Ny explains his doctrine (quoted as "the Sthavira" in the Ny) as follows:

There are only three caitta-s [i.e., vedanä, samjnä, cetanä].81 The samskära-skandha comprises cetanä alone — the samskära-s, manaskära, etc., all have cetanä as their intrinsic nature.82

The Commentaries explain that cetanä organizes its associated mental factors in acting upon the object. Its characteristic is the state of willing, its function is to accumulate (kamma), and its manifestation is coordination. Its proximate cause is the associated states. Just as a chief pupil recites his own lesson and also makes the other pupils recite their lessons, so when volition starts to work on its object, it sets the associated states to do their own tasks as well. Volition is the most significant mental factor in generating kamma, since it is volition that determines the ethical quality of the action.

Here [in the present life] with the maturing of the bases there is delusion, which is ignorance; there is accumulation, which is formations; there is attachment, which is craving; there is adoption, which is clinging; there is volition, which is being; thus these five ideas in being-as-action here are conditions for rebirth-linking in the future.

The 'choice' (cetana) here is the momentary mental 'willing' (or 'affirmation') at each and every stage of the 'course [of action]'.

It wills (cetayati), thus it is volition (cetaná); the meaning is that it arranges (collects) itself
together with associated states upon the object.

cetayati
Source: A.P. Buddhadatta Mahathera, Concise Pali-English and English-Pali Dictionary [available as digital version from Metta Net, Sri Lanka]
Description: cetayati : [cit + aya] perceives; thinks.

Cetanā [f. abstr. fr. cet, see cinteti] state of ceto in action, thinking as active thought, intention, purpose, will.  Defined as
action (kamma

Этакая деятельность сознания, постигающая объект.

Что тогда останется виджняне?

Intention directs the primary mind and associated mental factors to the object. Geshe Rabten describes
it as the ‘actual principle of activity.’ Therefore, he says, ‘Intention is karma itself.’