You have done foolishly: David speaks these same words about himself in 2 Sam 24.10. In English there is a great deal of difference in meaning between “you have acted foolishly” and “That was stupid!” (Contemporary English Version) or “You fool!” While the latter may sound quite strong, it is perhaps not too far from the meaning intended here.

You have not kept the commandment of the LORD: while this is stated negatively in the original, some languages may prefer to communicate the same meaning using a positive statement, “you have disobeyed [the command from] the LORD” or “you have disregarded the LORD’s rule.”

No commandment of the LORD to Saul has been previously mentioned in the story. Interpreters suggest various ways of understanding these words, but translators should not attempt to make explicit the content of the command. The Hebrew word translated commandment occurs only here in 1 and 2 Samuel. No distinction in meaning is intended between this noun and the Hebrew nouns “mouth” and “word,” also translated “commandment” by Revised Standard Version elsewhere in 1 Samuel.

For now … for ever: this clause expresses a condition contrary to fact, and the first part of the clause is left implicit in Hebrew. Good News Translation (also Parola Del Signore: La Bibbia in Lingua Corrente and Bible en français courant) makes the “if” part explicit by adding “If you had obeyed.” The sense is not that Saul himself would have ruled for ever if he had obeyed God. Rather God would have made sure that Saul’s descendants would have continued to rule. Revised English Bible says “If you had [kept the command of God] he would have established your dynasty over Israel for all time.”

Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 1. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .