Gerhard and Walther

A person must not only just look at food and drink but must also receive and partake of it if it is to be of benefit to him, so also we must not only know the Word of the Gospel about Christ and give approval to it. Instead, we must by true faith seize and take unto ourselves Christ as our soul’s spiritual food and drink. Through faith we can put on Christ, so that His righteousness becomes our cloak and decoration by which we are able to stand before God and please Him.—Johann Gerhard, Schola Pietatis II:205. 

Fellowship between orthodox and heterodox produces the following result: the orthodox become more indifferent to the errors of the heterodox, and the heterodox become more indifferent to the truth of the orthodox. Error triumphs and the truth is lost.—C. F. W. Walther, God Grant It!, p. 383.