Note how this is borne out at Romans 2:21-24:

“Do you, however, the one teaching someone else, not teach yourself? You, the one preaching ‘Do not steal,’ do you steal?

Teaching in God’s name requires the teacher to lead a life consistent with his “public declaration.” Suppose a father teaches his son “Do not steal.” But, then, what if the father himself behaves contrary to this, withholding income taxes or stealing from his neighbor? The man’s oral teaching will not likely convince his child. More importantly, the man is giving reason for “the name of God” to be “blasphemed.” So, real love for God’s name as well as effective teaching makes it mandatory that a Christian ‘practice what he preaches.’