BhajaGovindam

Kama krodhasya Lobhasya
Dehe tistanthi taskarah
Gnana ratnapa haraya
Tasmat jagrata jagrata

Explanation: This seemingly simple sloka from Adi Sankaracharya explains why even all men are born same why only few attain ultimate gnana.

Kama (sensuous desire), krodha (anger) , lobha (greed) are like thieves sitting in our body. Just like the task of thief is to steal the things, these internal thieves steal the precious jewel of gnana from you. In that case when should we be careful abt these thieves? Generally thieves come during nights so we would be carefully guarding our houses. But these internal don’t have such rule. They sit in our body and wait for an opportunity. So we need to be careful about them at all times.

Gnana here is said to be referring to realization of ultimate reality of God and not the bookish knowledge. Every knowledge that does not lead to bhakti and thus towards God is useless. This can be understood by his famous bhajagovindam song which Sankara sangs when he sees a old Brahmin reciting grammar. Int his context sankara says

BhajaGovindam Bhaja Govindam
Govindam Bhaja Mooda mate
Samprapte sannihite kale
Nah nahi rakshati dukkam karane

You fool pray to Lord Govinda. When you near your death these grammar rules cant save you from your sins. It may surprise some Sankara talks about Govinda(Vishnu) as Ultimate Reality here, in soundarya Lahari says Sakhti/Durga mata as Ultimate Reality and he himself is treated as Ultimate Reality ie., Lord Shiva. He so put forward Advaita School in which he says there is no duality of God. All the three forms mentioned are nothing but one and the same and they are seen in different forms depending on the function they are performing at that moment. Ultimate Reality is said to form less and is an experience that cant be described.
There are many questions left unanswered and it is up to the person to find the answers.