Also, we know that James 2:10 equates stumbling in one point with breaking them all, ("For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all."), but here Jesus is contrasting "Whosoever therefore shall break one of these least commandments, and shall teach men so" with "whosoever shall do and teach them," so He's putting an emaphasis on practicing obedience and teacing others to do the same.