11.  For it is not so easy to dye deeply a piece of cloth, or to impregnate with odours, foul or the reverse, whatever comes near to them; nor is it so easy for the fatal vapour, which is rightly called a pestilence, to infect the air, and through the air to gain access to living being, as it is for the vice of a superior to take most speedy possession of his subjects, and that with far greater facility than virtue its opposite.  For it is in this that wickedness especially has the advantage over goodness, and most distressing it is to me to perceive it, that vice is something attractive and ready at hand, and that nothing is so easy as to become evil, even without any one to lead us on to it; while the attainment of virtue is rare and difficult, even where there is much to attract and encourage us.  And it is this, I think, which the most blessed Haggai had before his eyes, in his wonderful and most true figure: Hagg. ii. 12 et seq.—“Ask the priests concerning the law, saying:  If holy flesh borne in a garment touch meat or drink or vessel, will it sanctify what is in contact with it?  And when they said No; ask again if any of these things touch what is unclean, does it not at once partake of the pollution?  For they will surely tell you that it does partake of it, and does not continue clean in spite of the contact.”