Too One Sided? I believe that Washer is trying to address an audience who treat theology as head knowledge but never transfer that knowledge into the heart. This sermon is probably right in the context of the audience that Washer aims to address.
However let us not play down the importance of theology. Where theology is right, men will go into the mission field. Where theology is wrong, men who rush into the mission field would burn out. We must enter into the mission field for Bible centred reasons.