What is the meaning of "Nothing new will be said here, nor have I any skill in composition. Therefore I do not imagine that I can benefit others."

To my knowledge, Bodhicaryāvatāra expressed the Nothing new will be said here, nor have I any skill in composition. Therefore I do not imagine that I can benefit others. I have done this to perfume my own mind.. In my limited understanding, it refers to the negative thoughts although I do not have complete comprehension of it. What does it refer to, what is the intention and what is to be practiced?