I made it through high school without ever encountering the subjunctive mood. Then I decided to learn French. I fought my way through the bewildering thicket of conjugations of regular and irregular verbs, then I was introduced to the subjunctive mood. My head hurt for weeks.
I didn’t seem to have any reference point in English to help me comprehend this way of expressing oneself, yet it seemed an essential part of French. Every English grammar book I looked at devoted about a paragraph to the subjunctive. They told me the subjunctive mood was on its deathbed in English and I would never have to worry about it.
Then an amazing thing happened: I finally got my head wrapped around the use of the subjunctive in French and I realized that it is still very much a part of English. So here I go where most grammarians fear to tread.
Subjunctive, from French, originally from Latin, means subjoined. (That little bit of information does nothing to understand it.) The best definition is from Oxford via Fowler’s: a verb form different from that of the indicative mood in order to denote an action or state as conceived (and not as a fact), and expressing a wish, command, exhortation, or a contingent, hypothetical or prospective event.

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When used to express a wish, a phrase in the subjunctive mood normally begins with let or may, though they me be omitted. All greetings are subjunctive:
– May God bless you!
– May you have a good day / May you have a happy birthday (even when shortened to Good day or Happy birthday, they are subjunctive).
– Good-bye (drastically shortened form of May God be with you).
Commonly used expressions in the subjunctive:
– Come what may
– Be that as it may
– Far be it from me
– I wish it were over
– If he were here now
– I move that nominations cease
– I move that we elect a committee to . . .
The Sunday School lessons that are used in the Church of God in Christ, Mennonite usually contain a sentence or two in the subjunctive mood; for example:
– Let us conduct ourselves accordingly
– May we never forget . . .
Examples of the subjunctive in the Bible:
– Hallowed be thy name, thy kingdom come, thy will be done (all three of these phrases in the Lord’s prayer are in the subjunctive mood).
– Let not your heart be troubled (let not . . . is found in many places in the Bible, it always indicates the subjunctive mood).
– Let no man despise thy youth (1 Timothy 4:12, Paul is expressing the wish that Timothy’s conduct would be such that no one would find fault with him because of his age).
– James 5:13, 14: Let him pray / let him sing psalms / let him call for / let them pray (these are all exhortations).
– Genesis 1: Let there be light, etc. (The creation account has many examples of God expressing a wish for something that was not a reality at the moment the wish was made, but immediately became reality.)
I hope this helps a little to understand the subjunctive mood, especially when it is encountered in the Bible. The translators did not drop in all those subjunctives to confuse us, they were subjunctive in the original Hebrew and Greek manuscripts; may they be less confusing to us as we recognize the subjunctive mood.