Only take care to you . . . keep your soul diligently . . . lest you forget what your eyes have seen . . . lest they depart from your heart . . . all the days of your life. (Deuteronomy 4.9)
All some of us have to do is look at sweets and we put on weight. While that adage is impossible, what does matter is whether we turn toward or away from the candy dish. The Hebrew ideas below explain how to turn away from the weight gain of idolatry.
“Only” comes from the root meaning “thin” or “in a slight way” which gives way to the concept of exclusivity: thin = only = single = lone. You can hear Yahweh say, “There is one way to react toward idolatry. What I’m about to say, is it.”
“Take care” in Hebrew has an ethical impact. Much like the word “see” above, the word keep is repeated: in this case, six times. The word means to watch, keep, guard, or protect. The implicit idea in this context is “pay careful attention.”
The focus of one’s attention is emphasized by using the same Hebrew verb again. Literally the text says “Watch you! Watch yourself!” Attitude is coupled with what one knows. A Hebrew would hear this and think “There is watching and then there is watching!” This is not an informational checklist. The command should impact one’s mindset. Proverbs 13:3 says to guard the mouth—think before you talk. Pay no mind to worthless idols is the sense of Psalm 31:6. Added to other verbs “watch” encourages the application of all a person’s faculties (Proverbs 4:21, 23 “kept in the heart”).
Watch “very closely” or “to the highest degree.” The first time the word is used in Scripture God saw all He had made and it was the best it could have been.  If used in military preparedness one would say, “We are Def Con 1—the highest state of alert.”
“Lest” forces the negative: don’t let it happen! Here is Yahweh’s injunction to prevent a theoretically possible event. Active remembrance of “the things that your eyes have seen” gives evidence for historical events. Memory retention, calling the past to mind, keeps one from deserting their post, turning aside from the way, avoiding responsibility, or ceasing their allegiance. Defection or apostasy is a potential for anyone. “Staying on the straight and narrow” is the point of the Hebrew “Do not turn aside to the right hand or the left.” The proper response is to “fear Yahweh and turn away from idols” (Ps 34:14; 37:27; Prov 3:7; 16:6, 17). Putting away idols (2 Kings 18:4; 2 Chr 30:14), strange gods (Gen 35:2), evil (Isa 1:16), false ways (Ps 119:29) and false worship (Amos 5:21-23) is the proper response for Deuteronomy’s injunctions.
The weight gain of idolatry always begins with our eyes. Our eyes–our focus, our attention on an object–can help us accept or reject eye candy. If we focus on idols, we gain the weight of worshiping another. If we focus on Yahweh, we stay thin; exclusively dedicated to a diet maintaining our attention on The One and Only True God.
Innocence is different than naivete. The second suggests one who is blind to trouble. The first identifies one who knows trouble but turns away. Mark has been teaching about idolatry, watching his weight, in Deuteronomy since 2009 at Crossroads Bible College.
 Genesis 6:5 “they were ONLY evil continually” or an exclamation thin = no more = stop, no further as in Numbers 20:19 “let me pass by on foot, nothing more.”
 Niphal imperative w/ ethical dative le “to you”
 Deuteronomy 4:2, 4, 6, 9 (2), 15.
 Gen 2:15; 3:24; 4:9
 The Hebrew word for “yourself” is nephesh meaning one’s person, one’s soul.
 Gen 1:31; 7:19; 13:13; 17:2; 27:33
 Holladay, 293. On “forget” see my page “Don’t Forget: Remedy for a Faulty Memory”
 Holladay, 254.
 From God: Deuteronomy 13:5; Isaiah 31:6; 59:13; Jeremiah 28:16; 29:32; from justice Deut 19:16.
 Deuteronomy 2:27; 5:32; Joshua 1:7; 2 Kings 22:2. Cf. Exodus 32:8; Deuteronomy 9:12; 11:16.