Single (απλους). Used of a marriage contract when the husband is to repay the dowry "pure and simple" (την φερνην απλην), if she is set free; but in case he does not do so promptly, he is to add interest also (Moulton and Milligan's Vocabulary, etc.). There are various other instances of such usage. Here and in Luke 11:34 the eye is called "single" in a moral sense. The word means "without folds" like a piece of cloth unfolded, simplex in Latin. Bruce considers this parable of the eye difficult. "The figure and the ethical meaning seem to be mixed up, moral attributes ascribed to the physical eye which with them still gives light to the body. This confusion may be due to the fact that the eye, besides being the organ of vision, is the seat of expression, revealing inward dispositions." The "evil" eye (πονηρος) may be diseased and is used of stinginess in the LXX and so απλους may refer to liberality as Hatch argues (Essays in Biblical Greek, p. 80). The passage may be elliptical with something to be supplied. If our eyes are healthy we see clearly and with a single focus (without astigmatism). If the eyes are diseased (bad, evil), they may even be cross-eyed or cock-eyed. We see double and confuse our vision. We keep one eye on the hoarded treasures of earth and roll the other proudly up to heaven. Seeing double is double-mindedness as is shown in verse Matthew 6:24.

Mt 6:24

No man can serve two masters (ουδεις δυνατα δυσ κυριοις δουλευειν). Many try it, but failure awaits them all. Men even try "to be slaves to God and mammon" (Θεω δουλευειν κα μαμωνα). Mammon is a Chaldee, Syriac, and Punic word like Plutus for the money-god (or devil). The slave of mammon will obey mammon while pretending to obey God. The United States has had a terrible revelation of the power of the money-god in public life in the Sinclair-Fall-Teapot-Air-Dome-Oil case. When the guide is blind and leads the blind, both fall into the ditch. The man who cannot tell road from ditch sees falsely as Ruskin shows in Modern Painters. He will hold to one (ενος ανθεξετα). The word means to line up face to face (αντ) with one man and so against the other.