In plain words
The secret way that brings well-being to mankind is to serve others without waiting to be served by them. That is, without hoping for any return. The axe that uproots the tree of karma is to do ‘all karmas to please God’. This is the chief yajña. The essence of this yajña is “Brahmavidyā”. The spirit of service must enter every nerve, every bone, every living cell of this body. Such a spirit of service must become second nature in every spiritual sādhana.