The first question that comes up is: Is this some kind of new-fangled grammar idea? No.
Fowler (1881) writes:
$ 517. Rule XXXIII.—Forms in the Imperative Mode have in English three peculiarities:
1. They have a simple form for the second person ; as, " Love thou ;" the third being expressed by a circumlocution; as, "Let him love." 2. They take pronouns after instead of before them; as, in the example given, "Love thou." 3. They often omit the pronoun altogether; as, "Love." . .
Passion goes at once to its object, assuming it as the consequence of an indirect assertion. Thus, if the fact be that I desire that a person should go to any place, it is not necessary for me to state my desire in the indicative mode, and his going in the infinitive, or subjunctive, or potential: "I desire you to go;" or, "I desire that you go;" or, "I desire that you should go;" but, by the natural impulse of my feelings, I say,"Go.'" Now this mode, from its frequent use in giving commands to inferiors, has been called the Imperative. Under this general term may be included not only a command; as, " Let there be light," but also a wish expressed; as, "Let confusion live;" and a prayer offered; as, "Help me, Lysander, help me;" and permission given; as, "Go, but be moderate in your food." In all of them the assertion of desire on the part of the speaker is clearly implied. The sense is, "I command that there be light;" "I wish that confusion may prevail;" "I pray you to help me;" " I permit you to go."Today, things have changed only slightly; no longer would we follow the verb with a subject: Get thou into thy cloister as the king Will'd it. Instead, usually we simply drop the subject altogether (though we can say You go to bed now.) The verb form, I believe, has not changed, though I would disagree with Fowler that is it the "simple form for the second person" and just call it base form of the verb.
"And God said, Let there be light: and there was light," shows a typical imperative. No subject, and the base form of 'let'. The shalt of the commandments, in contrast, is an inflected form: the second person indicative of shall. This can be seen when compared with Isaiah 1, 18 "though your sins be as scarlet, they shall be as white as snow;"
In Genesis 4, 12 we find, "When thou tillest the ground, it shall not henceforth yield unto thee her strength; a fugitive and a vagabond shalt thou be in the earth," which are again indicative, even though they have the rhetorical force of a command. Compare them to Genesis 6, 14: "Make thee an ark of gopher wood; rooms shalt thou make in the ark, and shalt pitch it within and without with pitch." The first clause here is imperative, lacking a subject and using the base form of 'make'. The second, though, shifts to the indicative.
Going back to the commandments, the two that are imperative are: "Remember the sabbath day, to keep it holy." and "Honor thy father and thy mother." All the others begin with the subject 'thou' and use second person indicative 'shalt'. Now it happens that the eight non-imperatives are all negative (i.e. thou shalt not). But they can be compared to Genesis 42, 22, "Do not sin against the child" which shows a true negative imperative.
Interestingly, in standard modern English (including that of King James) modal auxiliary verbs such as shall, will, can, etc. are defective; they have no base form or participles. They never appear in the imperative or in infinitive constructions. This is why you hear he should be able to do it but not *he should can do it.
In short, imperative mood isn't the only way to boss somebody around.