Every teacher teaches two lessons at a time - one from the lesson material and the other from himself. What he teaches from the lesson material often misses the mark; but the teaching that goes out from himself - his personality, his character, his life - goes without aim or effort straight to the hearts of his students. Children may fail to grasp the truth that comes from the teacher's lips, but they will not fail to absorb the truth that comes from the teacher's life.
It is not what the teacher teaches purposely or by earnest effort that goes deepest into the hearts of his students, but what he teaches unconsciously and without any purpose at all. It is not what the teacher says so much as what he is that makes for success in his holy calling.
So while it is extremely important to know your lesson and to have it well prepared, it is a far more important thing for you to know yourself and to have yourself well in hand.
Spend time preparing yourself. Find your way to the presence of the Master. Have Him cleanse your heart anew and fill you with His Spirit. Remain in His presence until your heart is in a glow and your face reflects the light that shines from His face; until all the harsher things in your nature disappear and love reigns supreme; until you are full of sweetness, gentleness, and loving kindness.
Climb by prayer up to the heights where petty things cease to vex; where it is easy to be patient; where trying circumstances are no longer trying; where one can suffer with a smile; where one can love the unlovely and the unlovable.
And always try to go to Sunday school by way of this mountain top.
Secrets of Sunday School Teaching
By Edward Leigh Pell