B.G 4.35
यज्ज्ञात्वा न पुनर्मोहमेवं यास्यसि पाण्डव। येन भूतान्यशेषेण द्रक्ष्यस्यात्मन्यथो मयि ॥३५॥
yajjñātvā na punarmohamevaṁ yāsyasi pāṇḍava। yena bhūtānyaśeṣeṇa drakṣyasyātmanyatho mayi ॥35॥
Having gained that knowledge, O Arjuna, you will never get deluded again. Possessed with such a knowledge, you will see all living beings residing in Me, without exceptions.
Gīta Bhāshya 4.35
Once you gain the stated knowledge, delusion disappears, and then you will see and understand - 'All living beings as residing in Me'.
The word 'yena', i.e. 'By which', is pointing towards 'that knowledge'. The word 'mayi', i.e. 'In Me', means reside in my 'ātman', i.e. residing in Me are all the living beings. The word 'atho', i.e. 'therefore', is used to indicate 'that is the way you will see' once the delusion is destroyed.