As stated in Śrīmad-Bhāgavatam (3.25.21):

"The symptoms of a sādhu are that he is tolerant, merciful and friendly to all living entities. He has no enemies, he is peaceful, he abides by the scriptures, and all his characteristics are sublime." Because Nārada Muni is the most elevated of sādhus, devotees, to deliver Prajāpati Dakṣa he silently tolerated the curse. Śrī Caitanya Mahāprabhu has taught this principle to all His devotees:"One should chant the holy name of the Lord in a humble state of mind, thinking oneself lower than the straw in the street; one should be more tolerant than a tree, devoid of all sense of false prestige and should be ready to offer all respects to others. In such a state of mind one can chant the holy name of the Lord constantly." Following the orders of Śrī Caitanya Mahāprabhu, one who preaches the glories of the Lord all over the world or all over the universe should be humbler than grass and more tolerant than a tree because a preacher cannot live an easygoing life. Indeed, a preacher must face many impediments. Not only is he sometimes cursed, but sometimes he must also suffer personal injury. For example, when Nityānanda Prabhu went to preach Kṛṣṇa consciousness to the two roguish brothers Jagāi and Mādhāi, they injured Him and made His head bleed, but nevertheless, He tolerantly delivered the two rogues, who became perfect Vaiṣṇavas. This is the duty of a preacher. Lord Jesus Christ even tolerated crucifixion. Therefore the curse against Nārada was not very astonishing, and he tolerated it.

Now, it may be asked why Nārada Muni stayed in the presence of Prajāpati Dakṣa and tolerated all his accusations and curses. Was that for Dakṣa's deliverance? The answer is yes. Śrīla Viśvanātha Cakravartī Ṭhākura says that after being insulted by Prajāpati Dakṣa, Nārada Muni should have left immediately, but he purposely stayed to hear all Dakṣa's strong words so that Dakṣa might be relieved of his anger. Prajāpati Dakṣa was not an ordinary man; he had accumulated the results of many pious activities. Therefore Nārada Muni expected that after delivering his curse, Dakṣa, satisfied and freed from anger, would repent his misbehavior and thus get a chance to become a Vaiṣṇava and be delivered. When Jagāi and Mādhāi offended Lord Nityānanda, Lord Nityānanda stood tolerantly, and therefore both brothers fell at His lotus feet and repented. Consequently they later became perfect Vaiṣṇavas.