Sentence:  At any rate , the <WSD>substance</WSD> of Eichmann 's testimony was that all his actions flowed from his membership in the party and the SS , and though the Prosecutor did his utmost to prove actual personal hatred of Jews , his success on this score was doubtful and the anti-Semitic lesson weakened to that extent . 
Meaning of the word marked with <WSD> tags:  the choicest or most essential or most vital part of some idea or experience