It seems common knowledge that Smriti (like the Puranas) is considered secondary authority to Shruti texts (like the Vedas).
But who decided that one is a greater authority than the other?
And if Smriti is considered more as 'tradition' and not as having divine origin, why is it given any authority? Again though, who decided that Smirit texts are not of divine origin?
Śrutī śastrās have their source in the Supreme Lord. Smrītī śastrās have been derived from Śrutīs.
Just like churning milk, we get it's essence - butter; similarly Smrītī texts, being the essence of śrutī śastrās and given to us by the seers and sages like the Rīśī & Munīs, are to be understood as the essence.
However, people differentiate between the two basis one being the origin of the other, thus considering Smrītī śāstras as less important/inferior to Śrutī śāstrās.
We shoud understand that both Smrītī & Śrutī are authorized Vedic literature. As both are non-different, they are both one in purpose - devotional service to Supreme Lord.
Srila Rupa Gosvami writes in his Bhakti-rasamrita-sindhu (1.2.101):
sruti-smriti-puranadi-
pancaratra-vidhim vina
aikantiki harer bhaktir
utpatayaiva kalpate
"Devotional service of the Lord that ignores the authorized Vedic literatures like the Upanishads, Puranas and Narada-pancaratra is simply an unnecessary disturbance in society."
Earlier, Vedic knowledge was handed down through an oral tradition, in spiritual disciplic succession, throughout the ages. However, for this age of Kali, when people can hardly remember what they did a week ago, or sometimes even yesterday, how would they be able to remember, analyze, comprehend, or follow the Vedic instructions if they were not in a written form.
Therefore, Vyasadeva - the literary Incarnation of Supreme Lord, appeared as the person qualified to compile it and form its many branches.
Vyāsadeva composed the more important Vedic texts, culminating in his own commentary of the Vedic writing in the form of the Srimad-Bhāgavatam. In this way, the one Veda became the four main samhitas, namely the Rig, Yajur, Sama, and Atharva Vedas. Then came the Brāhmana texts, the Vedānta Sutrās, the Mahābhārata, and then the Purānas, of which Vyāsadeva considered the Bhagāvata Purāna (Srimad Bhagavatam) the most important and complete. In this way, the essence of the Absolute Reality is to be found in the Vedic literature, especially within the Srimad-Bhagavatam.
Śrimad Bhāgavatam is known as the spotless Purāna. It is said to be the ripe fruit on the tree of Vedic knowledge.
nigama-kalpa-taror galitaḿ phalaḿ
śuka-mukhād amṛta-drava-saḿyutam
pibata bhāgavataḿ rasam ālayaḿ
muhur aho rasikā bhuvi bhāvukāḥ
O expert and thoughtful men, relish Śrīmad-Bhāgavatam, the mature fruit of the desire tree of Vedic literatures. It emanated from the lips of Śrī Śukadeva Gosvāmī. Therefore this fruit has become even more tasteful, although its nectarean juice was already relishable for all, including liberated souls. [S.B. 1.13]
