"The Lord God has sworn by His holiness" - Although not in the habit of swearing oaths—His Word is sufficient—God sometimes does so to focus on the seriousness of a pronouncement. As the writer of Hebrews says, "For when God made a promise to Abraham, because He could swear by no one greater, He swore by Himself" (Hebrews 6:13).
What does God see in Israel that so affronts Him that He has to swear "by His holiness"? Israel had every opportunity that the Gentiles did not have: His calling, His promises, His Word, His laws. He gave the Israelites these gifts to help them develop into His sons and daughters, but God sees them as diametrically opposite of Himself. Should not God expect to see some of His characteristics in His sons?
A simple illustration from the author's experience in visiting a family may help in understanding this point. Parents often show their pride by prominently displaying a photograph of their children, and these parents were no different. In this case, three of the four children bore a strong resemblance to their parents, but the fourth child was so noticeably different that it was obviously either an adopted child or the product of adultery.
God says, "I have children who bear no spiritual resemblance to me." He shows the cause to have been spiritual adultery—going after other gods and other ways of life.
"I have nourished and brought up children, and they have rebelled against Me; the ox knows its owner and the donkey its master's crib; but Israel does not know, My people do not consider." Alas, sinful nation, a people laden with iniquity, a brood of evildoers, children who are corrupters! They have forsaken the Lord, they have provoked to anger the Holy One of Israel, they have turned away backward. (Isaiah 1:2-4)
A dumb ox and donkey show more sense and appreciation to their masters than Israel did to her Father! Instead, she rebelled against Him!
God gave Israel many advantages—His law, His providence, His protection—to allow His people to live His way of life, but they turned their backs on Him and followed the ways of other gods. Paul shows how illogical this is:
For even if there are so-called gods, whether in heaven or on earth (as there are many gods and many lords), yet for us there is one God, the Father, of whom are all things, and we for Him; and one Lord Jesus Christ, through whom are all things, and through whom we live. (I Corinthians 8:5-6)
Since we have complete dependence upon God for life as our Designer, Lifegiver, and Sustainer, He has complete authority over how we should live. Among the multiple pantheons of gods, only one God lives the way a God ought to live. This particular God—the God of Israel—is holy, that is, He alone is transcendentally different, superior, and separate. He has called His people to be holy (I Peter 1:15-16). It follows that a holy person must be different in the way that God is different.
From God's holiness flows His love—outgoing concern for others, His outstanding attribute. When God looked on Israel, however, He saw a whole nation, from her culture to her government to her religion, organized on the basis of human self-concern. God wanted to see clear evidence of godly living, by which He could verify their claims of being His people. In Israel, He saw no such evidence, but instead a people in opposition to Him in every area of life. Spiritual adultery had occurred.