Prof. Cousins emphasizes the meditational aspect:
This brings me to the very large number of passages in which kusala is linked with dhamma, either in the singular or more often in the plural. It is important to note that many of the passages here are meditational in their orientation. So in the Mahāvagga (Vin I 104) the Buddha declares that if a monk does not make known a Vinaya offence when the Pātimokkha is recited, this would be a deliberate lie and a deliberate lie is an obstacle. The text defines an obstacle (antar āyiko dhammo), first of all as an obstacle to achieving the first jhāna, then successively to the remaining jhānas up to the fourth, then various kinds of meditational experience are mentioned, ending (summarizing) with "to the achieving of skilful dhammas." Similarly, in the discussionof the fourth pārājika (at Vin ĪI 91), in the list of higher states which must not be falsely claimed by the monk these meditational attainments (jhāna, vimokkha, samādhi, etc.) are referred to as skilful dhammas.
This kind of direct linkage between higher states and skilfulness is found in a number of contexts.(35) So in the Saṃyutta-nikāya we find the ascetic who wishes to attain a skilful dhamma and realize higher states (uttari-manussa-dhamma; alam-ariya-ñāṇa-dassana). In the Lohicca-sutta we meet the idea that if someone attains a skilful dhamma, he should not tell anyone else. Or the Buddha is asked if he has achieved this skilful dhamma for a long while. Again in the A"nguttara-nikāya we learn of the six factors which make a monk fit (or unfit) to attain a skilful dhamma: he is skilful in coming, skilful in going, skilful as to means (upāyakusala), he arouses the purpose (chanda) of attaining a skilful dhamma which has not been attained, he guards skilful dhammas which have been attained and is successful in constant action. Compare too passages in which are found the expression: (he succeeds in) the method, the dhamma that is skilful (...ñāyaṃ dhammaṃ kusalaṃ).(36) Usually this makes the point that, whether householder or renunciant, he can succeed if he follows the right way i.e. the eightfold path.
Similar usages occur in the plural too.(37) So in the Majjhima-nikāya, when the Jains admit to not knowing: "the arousing of skilful dhammas", the reference must be to the apparent absence of the higher jhānas in the Jain system.(38) Or, in the A"nguttara-nikāya, when skilful dhammas explicitly refer to mental peace (cetosamatha) within and insight into dhammas from the standpoint of wisdom (adhipaññādhammavipassanā). In the Paṭisambhidā-magga we are even told that all skilful dhammas lead in the direction of the liberations (vimokkhānuloma).
There are a great many places in which skilful dhammas are referred to briefly or without much qualification, where it is not possible to be sure whether the intention is to refer specifically to meditational states. Nevertheless, this is probably the meaning which should be assumed in the majority of cases. I do not wish to argue that a broader usage which includes other desirable states is entirely excluded, only that in such cases the expression points primarily to meditational practice. This makes translation by such expressions as "good states " misleading; for such renderings point first and foremost to the ordinary ethical dimension and only secondarily to meditational experience. By contrast I believe the intention of the Pali texts in these passages is to point first to the jhānas and the states later known as the dhammas contributing to awakening (bodhi-pakkhiya). In other words the use of kusala in these contexts is concerned with the fact that these are special states which are, directly or indirectly, produced by wisdom. That is why they are called "skilful".
There are equally a great many passages where the meditational context is beyond real dispute. One example of this is the occurrence of skilful dhammas in the formula of the four right efforts and in related formulae concerned with vigour (viriya), such as descriptions of effort (vāyāma) in the eightfold path.(39) This of course is simply a specific case of the bodhi-pakkhiyas in general and indeed the seven sets are sometimes cited in relation to
But, Venerable sir, there is another incomparable quality (ānuttariya): how the Lord teaches dhamma as regards skilful dhammas. As to that, the skilful dhammas are as follows: four establishings of mindfulness, four right efforts, four bases of success, five faculties, five powers, seven factors of awakening, the noble eightfold path ... That, Venerable Sir, is an incomparable quality as regards skilful dhammas ... there is nothing further to be known by higher knowledge, such that another mendicant or brahmin, knowing by higher knowledge, would know more deeply i.e. as regards skilful dhammas.(40)
Sometimes the link is made directly to the first of the seven sets: the four establishings of mindfulness.(41) So for example in the Janavasabha-suttanta we are told by Brahmā Sanaṃkumāra that the four establishings of mindfulness were made known for the purpose of attaining the skilful -- here the reference must be to the remaining six sets. Some at least of the discourses, where things kusala are mentioned in a context which lead up to a culmination with the eightfold or the tenfold path, probably belong here.(42) Compare also the Kāya-gatā-sati-sutta where we are told, in relation to the person who has brought into being, made much of and immersed himself in mindfulness of the body, that whatever skilful dhammas he has are connected with the knowledges (vijjā-bhāgiya) i.e. lead to the three knowledges.(43)
When in the Mahā-hatthi-padopama-sutta Sāriputta tells (M I 184) us that all skilful dhammas are included in the four noble truths, we should again interpret skilful dhammas here as referring to meditational states. Indeed, this is made clear later in the sutta by the references to equipoise connected with the skilful. More generally, there are many passages in which skilful dhammas are spoken of in association with bhāvanā "bringing into being" or some form of the verb bhāveti.(44) In most of these what is implied is the technical sense of these words, as referring to the bringing into being of the eightfold path in particular or the dhammas which contribute to awakening in general i.e. the fourth noble truth. This is even more likely to be the case when the skilful to be brought into being is contrasted with the unskilful "to be abandoned" i.e. the corresponding function of the second noble truth.(45) No doubt closely related to this is the idea of achieving a stage of fixity in relation to skilful dhammas, an idea closely related to some interpretations of what is meant by stream-entry.(46)
There are a number of passages which refer to someone who is (not) applying insight (vipassaka) to skilful dhammas.(47) Sometimes this probably refers to a type of insight meditation.(48) However, it also merges into contexts where skilful dhammas or the skilful is simply the object of doubt or wisdom.(49)
Skilled in meditational/mystical (/ascetic?) practices (in the early Pali sources and, no doubt, in other contemporary traditions), including skilled in the kind of behaviour which supports meditation, etc. i.e. sīla, etc.http://www.buddhistethics.org/3/cousins1.html