Charles Ellicott Commentary 1 Samuel 20:12

"And Jonathan said unto David, Jehovah, the God of Israel, [be witness]: when I have sounded my father about this time to-morrow, [or] the third day, behold, if there be good toward David, shall I not then send unto thee, and disclose it unto thee?" — 1 Samuel 20:12 (ASV)

O Lord God of Israel. — Now that the two friends have come to a remote, solitary spot, Jonathan prefaces his reply to David’s pitiful request with a very solemn invocation of that God they both loved so well. The vocative, however, “O Lord God,” etc., from the English Version, has generally been regarded as an impossible rendering—“there being no analogy for such a mode of address”—Lange.

The versions avoid this by supplying different words. So the Syriac and Arabic render, “The Lord of Israel is my witness”; the Septuagint, “The Lord God of Israel knows.” Others have supplied a word they find in two Hebrew MSS., “As the Lord God of Israel liveth.” The meaning, however, is perfectly clear.

Or the third day.— This statement of time from Jonathan evidently assumes that the festival continued the day after the “new moon” with a royal banquet. The time is reckoned as follows: the present day; the next day, which was the new moon festival; and the day after that, which would be counted as the third day.

Behold, if there be good toward David. — If the news were good—that is, if Saul, contrary to David’s expectation, spoke kindly of him—then Jonathan would send a special messenger to him. If, on the other hand, the king displayed enmity, in that case, Jonathan would come himself and see David (for the last time). This sad message was to be brought by no messenger.