Because the Lord would save Judah, the prophet advised against a confederacy with other nations for security; the king and people should make the Lord their “sanctuary.” Isaiah knew, however, that the Lord as Savior in those times, as also later during the Lord’s life on earth, would be “a stone of stumbling,” upon whom many unbelievers would “stumble, and fall, and be broken, and be snared, and be taken” (Isa. 8:14–15).
Neither the king nor the people would accept the testimony given to the Lord’s disciples, nor would they understand the “signs” and wonders provided through Isaiah.
(Ellis T. Rasmussen, A Latter-day Saint Commentary on the Old Testament [Salt Lake City: Deseret Book Co., 1993], 510.)
The phrase “both the houses of Israel” refers to the northern kindgom of Israel and the southern kingdom of Judah. During times of apostasy, citizens of these kingdoms viewed Jesus Christ as a stumbling stone, or someone who got in their way during their journey through mortality.
(Donald W. Parry, Visualizing Isaiah,[Provo, Utah, The Foundation for Ancient Research and Mormon Studies, 2001], 77.)
Both Peter and Paul quoted verse 14 to the Jews as evidence of their stumbling over Christ (see 1 Pet. 2:8; Rom. 9:33; 1 Cor. 1:23). Jacob, the Book of Mormon prophet, also foretold that the Jews would stumble over Christ (see Jacob 4:15).
(Monte S. Nyman, Great Are the Words of Isaiah [Salt Lake City: Bookcraft, 1980], 65.)