In verse 5 your keeper uses the same word “to keep” used in verses 3b, 4a; and your shade means “your protection,” a meaningful figure of speech in a land where the shade of a tree would protect the traveler from the harmful effects of the hot sun (see “shadow” in 91.1b). On your right hand means “close to you, near you, at your side.”

In verse 6 Yahweh is said to afford protection from The sun and the moon. The sun’s intense heat can be harmful, and it was believed that the rays of the full moon were dangerous, causing epilepsy and other diseases. (A reflection of this belief is seen in the word “lunacy,” which comes from the Latin word for “moon.”) The verb smite can be translated in a more general way, “hurt, harm, injure.” It may be necessary to be specific in regard to the harm of the sun and say, for example, “The sun will not burn you in the daytime.” Both Good News Translation and Revised Standard Version use ellipsis in nor the moon by night. Obviously, if the translator has used “burn” in connection with the sun, it cannot be used with the moon. This is the advantage of using a generic verb with the sun. In languages where ellipsis cannot be used, the translator must consider carefully the use of a specific verb in relation to the moon. Since a great variety of beliefs and customs are associated with the moon and its phases, it may be necessary to provide a note to say that verse 6 means that God protects people both day and night.

Quoted with permission from Bratcher, Robert G. and Reyburn, William D. A Handbook on the Book of Psalms. (UBS Helps for Translators). New York: UBS, 1991. For this and other handbooks for translators see here .