Sentence:  The next traditional step then was to accept it as the authoritative textbook of the Christian faith just as one would accept a treatise on any earthly `` science '' , and I submitted to its conditions according to Christ 's invitation and promise that , `` If any man will <WSD>do</WSD> his will , he shall know of the doctrine , whether it be of God , or whether I speak of myself '' ( John 7 : 17 ) . 
Meaning of the word marked with <WSD> tags:  engage in