Hare Raam Hare Krishna

Raam and Krishna had many names

Like raam was known as dashrathnandan, purushottam , etc.

Similarly Krishna was also known as kanha,yashodanandan,etc.

Since it was difficult to remember al the names, our ancestors created two arrays

Array[Raam] and Array[Krishna]

and assigned all the names to these two arrays

From then they started singing Array(Hare) Rama, Array(Hare) Krishna