In plain words
That is the Ānanda that is eternal and true. The Taittirīya Upaniṣad has compared such lasting Ānanda to a bird. To the head of this bird it gave the name śraddhā, to the right wing Ṛta, to the left wing Satya, to the middle of the body yoga, and to the tail mahattattva. Man attains lasting Ānanda only when he develops these five limbs: śraddhā, Ṛta, Satya, yoga and mahattattva.
Tāraka and māraka
Because śraddhā is so very important, it has been compared to the head. For every living being śraddhā is the chief thing and the standard. In the Bhagavad Gītā too it has been said, “The one who has śraddhā gains Jñāna.” Not only that. “I Myself am the embodiment of śraddhā,” said Kṛṣṇa Paramātma. One who has no śraddhā cannot accomplish any task, however small. Above all, on the spiritual path śraddhā is essential. Śraddhā is nothing but firm, lasting, unshakeable faith. The Upaniṣads have declared that Jñāna joined with śraddhā is tāraka, and that Jñāna without śraddhā is māraka. They have taught that in spiritual matters śraddhā itself is the tāraka mantra. The tāraka mantra means what does not change in the three times. Man must keep such a tāraka mantra fixed in his heart. This is the chief principle of the Taittirīya Upaniṣad. Man gains true Jñāna only when he develops śraddhā, Ṛta, Satya, yoga and mahattattva and makes his heart pure. Jñāna does not mean acquaintance with books. “The vision of non-duality is Jñāna.” Non-duality lies contained within duality itself. The Taittirīya Upaniṣad teaches just such a supreme truth.
The example of Ubhayabhāratī
Ādi Śaṅkara, spreading the doctrine of Advaita, made a journey of victory from the Setu to the Himālaya. When he went to the northern lands, he met a great scholar there named Maṇḍana Miśra. In the debate of argument and counter-argument held between the two of them, Maṇḍana Miśra was defeated. Maṇḍana Miśra's wife was Ubhayabhāratī. She was endowed with every kind of knowledge. Śraddhā, Ṛta and Satya, all three, were in her.