Anticipating a laxity towards dharma in Kali Yuga, Lord Krishna had asked Bhishma, lying on the bed of arrows awaiting his death, to expound his views on dharma and governance and share his knowledge with the Pandavas, so that they be passed on down the line and be preserved. 
Bhishma was moved when Krishna, along with the Pandavas, visited him and blessed him during the final moments of his life. 
Thus Bhishma deemed it a great honour to restate the ideals, moral codes and the best of spiritual practices, in the presence of Krishna, not just for Yudhishtir and his brothers to follow. 
The Lord wanted these values to be available down the line for ever and to be preserved among the people.  
The Puranas stating on the four yugas on life, that in the Krita Yuga, dharma is on top, while there is a gradual deterioration of moral values through the Treta, Dwapara and Kali Yugas. The scene in Kali Yuga does not lend itself to giving primacy to a life of virtues and dharma, and few people look up to God. Therefore, Krishna wanted Bhishma to reiterate these core values, said Sri L Sampathkumar in a discourse.
In the Santi Parva, Bhishma dwelt on morals and ethics and how it was important that people stuck to these ideals. 
Bhishma stressed that dharma is the foundation of universal order. To be relieved from the cycle of birth, one must worship God with total devotion, especially in Kali yuga. Devotion to God will save one from the evils of sin, anger, hatred and greed. The various names of the Lord and the various forms were meant to help people concentrate better during their meditation, Bhishma added.