In plain words
The ways of these three run as the flow of prāṇa into the flow of apāna, the flow of apāna into the flow of prāṇa, and kumbhaka in both of these, the flow of prāṇa and the flow of apāna.
Pratyāhāra means setting out to bring inward the feelings of the senses, which face outward: that is the special value of pratyāhāra. That is, because the rays of the mind spread over the scenes of nature, the mind grows impure; and because it develops its attachment only to desires bound up with the objects of the senses, he becomes bound. For that reason, the meaning of pratyāhāra is precisely the effort to turn these rays of the mind back toward the mind. But today many sādhakas, because they follow gurus who do not fully know, pass their time in their daily round, some doing only prāṇāyāma, others following only pratyāhāra. This is a great mistake. Pratyāhāra without prāṇāyāma, or prāṇāyāma without pratyāhāra, cannot be done. Prāṇāyāma and pratyāhāra, both of them, are like a pair. These two are like an object and its reflection. If we do one without the other, its fruit will not come to us. Only when we restrain the mind does the prāṇa, too, come under control. Only when we restrain the prāṇa does the mind come under control. In the two, the mind and the prāṇa, the body stands as a form of consciousness. So, to bring this consciousness of the body to a standstill, we practise both, the mind as inward vision and prāṇāyāma that restrains the prāṇa; only then does what is called the attainment of samādhi come to us.
The second line tells us that, in this, examining the eternal and the transient is what matters. When we examine the eternal and the transient, it becomes clear that the Ātma is Satya and the body Asatya. When the inquiry into the Ātma is carried out well, this Ātma also has the names ‘Satyaṃ Śivaṃ Sundaraṃ’, full of meaning. There can be no Śivam without Satyam, and no Sundaram without Śivam. Śivam is the very light of Satyam. Sundaram is the very grace of Śivam. Satyam is like light. Only through light are we able to see Prakṛti.