From time immemorial, the Guru imparts the Spiritual Knowledge to his disciple provided the disciple is deserving.In the Gurukul system of India, the disciples used to serve the Guru in addition to learning.The Guru would impart the knowledge looking at the capacity of the disciple.Today you can buy “literacy” for money.
The Guru is like an “Ocean” of knowledge. Imagine a weak person going to an ocean with only two buckets to fetch water.He will get only two buckets of the ocean water and nothing more.So in ancient India, the Guru would judge the capacity of his disciple and impart as much knowledge as he could grasp.
So here Lord Krishna says in the second verse and the current one that this knowledge was lost because there were no deserving students and it broke the lineage of Guru-disciple transmission.So anything that becomes scarce becomes secret.So Lord Krishna says – Today “I” have given you this ancient and secret knowledge to you because of are a deserving candidate.
devadasnayak 