I hate to just steal posts, but Susan was pointing people to this Walther quote posted by Elephant's Child. It is a great simple explanation of why purity of doctrine should be foremost concern.
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"It is true, brethren, as you well know, that in our day it is common for people to say, 'Emphasizing doctrine so much only harms and hinders the kingdom of God, yes, even destroys it.' Many say, 'Instead of disputing over doctrine so much, we should much rather be concerned with souls and with leading them to Christ.' But all who speak in this way do not really know what they are saying or what they are doing. As foolish as it would be to scold a farmer for being concerned about sowing good seed and to demand of him simply to be concerned about a good harvest, so foolish it is to scold those who are concerned first and foremost with the doctrine, and to demand of them that they should rather seek to rescue souls. For just as the farmer who wants a good crop must first of all be concerned about good seed, so the church must above all be concerned about right doctrine if it would save souls."
(C. F. W. Walther, “Our Common Task: The Saving of Souls” , Essays for the Church [Saint Louis: Concordia Publishing House, 1992], Vol. I)