If Krishna is self-sufficient then why did He create us? Is it to serve Him?
Yes, Krishna is self-sufficient, however we are not self-sufficient. He is perfect, however we are not. He is self-satisfied, however we are not. He is completely independent, however we depend on Him. It was our desire to be separate from the Lord, therefore He has created this material world. He never created us. Both the Supreme Lord and the living entities eternally exist. Only thing is that we forget, however He never forgets us. He wants us to come back to Him as quickly as possible. He doesn’t like His children to be suffering in this material world in forgetfulness of Him.
Just like father feels happy when the child offers him a flower or a small gift on his birthday. Similarly, Supreme Lord feels happy, when someone makes a small gesture of service toward Him. We have not realized how much pleasure is there in serving Him. We are trying to serve family, nation, community and many others, however we are not satisfied at all by serving them. Because all of them are like leaves of the tree. A tree can not be nourished by pouring water on the different branches, fruits or leaves of the tree. However, when someone waters at the root of the tree, all the leaves, branches and fruits are properly nourished. Supreme Lord Krishna is the root cause of everything. Many devotees in the past have served Lord Krishna and achieved perfection of their lives. Therefore, it is better and safer to serve Krishna than to serve material agents and prolong our existence in this material world.