[924] The Eye Lamp Body Parables: Simple Minds or Single Minds

22 The lamp of the body is the eye. If ever therefore may be the eye of you single/simple, whole the body of you bright will be;
23 if ever but the eye of you wicked may be, whole the body of you dark will be. If therefore the light the (one) in you darkness is, the darkness how much. (Matthew 6 )

34 The lamp of the body is the eye of you. Whenever the eye of you single may be, also whole the body of you enlightened is; whenever but wicked it may be, also the body of you dark.
35 Be alert therefore not the light the (one) in you darkness is. (Luke 11 )

LIDDELL AND SCOTT has

L5151  a`plo,oj  aplooj  a`plo,oj, h( on, contr. a`plou/j, h/( ou/n (from a[ma, as Lat. simplex from simul, opp. to diplo,oj, duplex, twofold).

I. single, Sophocles., Thucydides.

II. simple, natural, plain, sincere, frank, Trag., Plato., etc.: in bad sense, simple, Isocrates.

III. simple, opposite to compound, Plato.; a`plh/ dhmokrati,a sheer democracy, Idem.

2. simple, absolutely true, Idem.

IV. Adverb. a`plw/j, v. sub voc.

V. Comparative and Superlative. a`plou,steroj( a`plou,statoj.

Literally the word aplouj is SINGLE although it can also mean simple. 

The eye, here is the eye of the mind. did not want us to be simple minded. He wants us to be single minded in our priestly service to him.

So if you serve God with you WHOLE mind. Then it will be SINGLE. And you will be serving only one master. It is a simple parable. But really powerful

Simple Minds is one group. Single Minds is another.