As mentioned above, the Śvetāśvatara Upaniṣad (3.19) states:

apāṇi-pādo javano grahītā
 paśyaty acakṣuḥ sa śṛṇoty akarṇaḥ
sa vetti vedyaṁ na ca tasyāsti vettā
 tam āhur agryaṁ puruṣaṁ mahāntam

This Vedic mantra clearly states, puruṣaṁ mahāntam. The word puruṣa means “person.” In the Bhagavad-gītā (10.12) Arjuna confirms that this person is Kṛṣṇa when he addresses Kṛṣṇa as puruṣaṁ śāśvatam: “You are the original person.” Thus the puruṣaṁ mahāntam mentioned in the verse from the Śvetāśvatara Upaniṣad is Śrī Kṛṣṇa. His hands and legs are not mundane but are completely transcendental. However, when He comes, fools take Him to be an ordinary person (avajānanti māṁ mūḍhā mānuṣīṁ tanum āśritam). One who has no Vedic knowledge, who has not studied the Vedas from a bona fide spiritual master, does not know Kṛṣṇa. Therefore he is a mūḍha. Such fools take Kṛṣṇa to be an ordinary person (paraṁ bhāvam ajānantaḥ). They do not actually know what Kṛṣṇa is. Manuṣyāṇāṁ sahasreṣu kaścid yatati siddhaye. It is not possible to understand Kṛṣṇa simply by studying the Vedas perfectly. One must have the mercy of a devotee (yat-pādam). Unless one is favored by a devotee, he cannot understand the Supreme Personality of Godhead. Arjuna also confirms this in the Bhagavad-gītā (10.14): “My Lord, it is very difficult to understand Your personality.” The less intelligent class of men cannot understand the Supreme Personality of Godhead without being favored by His devotee. Therefore the Bhagavad-gītā (4.34) contains another injunction:

tad viddhi praṇipātena paripraśnena sevayā
upadekṣyanti te jñānaṁ jñāninas tattva-darśinaḥ

One has to approach a bona fide spiritual master and surrender to him. Only then can one understand the Supreme Personality of Godhead as a person.