Do Not Lie to One Another, since You Have Put Off the Old Man With His Deeds
You shall destroy all those who utter a lie (Ps. 5:7). The mouth that speaks a lie will slay the soul (Wis. 1:11)
Forasmuch as all sins arise through a love of pleasure or avarice or vainglory, we can say that lying has its roots in these three vices: a man has to avoid blame and humiliation to fulfil his own desires or to gain something …And in the end no one believes him when he speaks the truth …A man whose very life is a lie is one who is licentious and pretends to be temperate, or a miser and speaks of almsgiving and compassion, or ostentatious and goes in raptures over poverty, not wanting to acquire the virtue he praises …’the devil changes himself into an angel of light‘ (II Cor. 11:14) …the man whose very life is a lie: he is not a simple but a two-faced man; he is one thing on the inside and another on the outside.
St. Dorotheos of Gaza. Discourses, IX. On Falsehood. B#45, pp160-162