21.  The soul is self-governed:  and though the devil can suggest, he has not the power to compel against the will.  He pictures to thee the thought of fornication:  if thou wilt, thou acceptest it; if thou wilt not, thou rejectest.  For if thou wert a fornicator by necessity, then for what cause did God prepare hell?  If thou were a doer of righteousness by nature and not by will, wherefore did God prepare crowns of ineffable glory?  The sheep is gentle, but never was it crowned for its gentleness:  since its gentle quality belongs to it not from choice but by nature.