It was. Omit these words and supply Ellipsis by adding, with Septuagint, "Before Jehovah [did. dance]".
Related Commentaries of 2 Samuel 6:21
2 Samuel 6:21
21 And David said unto Michal, It was before the LORD, which chose me before thy father, and before all his house, to appoint me ruler over the people of the LORD, over Israel: therefore will I play before the LORD.