This chapter of 35 verses deals with the body and spirit in the first half, and for the rest, about Prakruti (Nature) and Purusha (Supreme Spirit). One might notice that v10, advocating asceticism to which Krishna was opposed, won't jell with the rest, either contextually or philosophically, and thus should be seen as an interpolation.
V22, which states that the Supreme Soul lay in beings as a sustainer, consenter, enjoyer and overseer, contravenes its very nature expostulated in Ch15, v16-v18. Besides, as can be seen, it also affects the continuity between v21 and v23 in this, and v30, akin to v15 is an irrelevant interpolation.
It may be noted that inexplicably though, the first verse of this chapter, is either omitted from some texts or retained, but traditionally 'unnumbered' in others, for reasons none explained, which reads thus:
Ch13, V0
Thus spoke Arjuna:
What is nature 'n its role,
What is spirit 'n its nature,
What is frame 'n who lords it
What makes feeling 'n sixth sense?
arjuna uvācha
prakṛitiṁ puruṣhaṁ chaiva kṣhetraṁ kṣhetra-jñam eva cha
etad veditum ichchhāmi jñānaṁ jñeyaṁ cha keśhava
So be it, now to,
V10
asaktir anabhiṣhvaṅgaḥ putra-dāra-gṛihādiṣhu
nityaṁ cha sama-chittatvam iṣhṭāniṣhṭopapattiṣhu
Single-pointed devotion in me through unwavering yoga, going to solitary locations and disinterest in the assembly of people.
Maybe it's a way for Nirvana but certainly out of place in the context of Krishna motivating Arjuna to fight a just war, and thus should be seen as an interpolation. Before going to the interpolated v22, a reading of its preceding and succeeding verses is needed to appreciate its digressive nature.
Ch13, V20
It's Nature that tends beings
Binding Spirit to one's own acts
prakṛitiṁ puruṣhaṁ chaiva viddhy anādī ubhāv api
vikārānśh cha guṇānśh chaiva viddhi prakṛiti-sambhavān
Ch13, V21
Spirit that lay in beings all
Inclines to one's attitudes,
With the ethos it imbibes
Tends it one to like rebirth.
kārya-kāraṇa-kartṛitve hetuḥ prakṛitir uchyate
puruṣhaḥ sukha-duḥkhānāṁ bhoktṛitve hetur uchyate
V22
puruṣhaḥ prakṛiti-stho hi bhuṅkte prakṛiti-jān guṇān
kāraṇaṁ guṇa-saṅgo 'sya sad-asad-yoni-janmasu
He who is the witness, the permitter, the nourisher, the experiencer, the master and who is also spoken of as the supreme self, is the supreme Purusha in this body.
Ch13, V23
Gets one freed, as he grasps
Aspects Nature 'n Spirit as well.
upadraṣhṭānumantā cha bhartā bhoktā maheśhvaraḥ
paramātmeti chāpy ukto dehe 'smin puruṣhaḥ paraḥ
Hence, owing to its digressive nature v22 is an interpolation.
Then to
V30
prakṛityaiva chakarmāṇi kriyamāṇāni sarvaśhaḥ
yaḥ paśhyati tathātmānam akartāraṁ sa paśhyati
When he realizes that the variety of beings is established in the one, and it is only an evolution of that (one), he then attains brahman. It can be seen that the above is akin to v15 of this chapter and thus it is an irrelevant interpolation as well.
Ch13, V15
In beings all 'n objects too
Within He lies, without as well,
If one comes to grasp this well
It's perception that's Supreme.
ṛiṣhibhir bahudhā gītaṁ chhandobhir vividhaiḥ pṛithak
brahma-sūtra-padaiśh chaiva hetumadbhir viniśhchitaiḥ