Spiritually qualified rulers...

Verse 1.12.15-16 (Yugal Kishore Pr):
* Dharma means the laws enunciated by the Lord. And what the Lord says is dharma.
* There needs to be a nice ruler to uphold these laws. The supreme Lord always wants a nice spiritual ruler. Since no one else was present, Lord Krishna wanted to protect Maharaj Parikshit.
* Vishnu is an expansion of Lord Krishna, for protecting the devotees. So here, to protect His devotee's heir, Lord Krishna took the form of Vishnu. It is His special mercy to His devotees.
"Lord Krishna, the original Personality of Godhead, does the work of protection and annihilation in His capacity of Visnu. Lord Visnu is the plenary expansion of Lord Krishna."
* Also, to make the future generation relish the pastimes of Krishna, He performs wonderful pastimes.
* In Kaliyuga, there are no such rulers to protect the laws of the Lord. Thats why lot of mercy is given. And that is given through chanting of the holy name. Every mantra, we should plead to the Lord through His holy name.
* We also need to develop a lot of patience also in chanting.