This post was first published in June, 2020. —ed.
We can’t fully understand God’s holiness. But we can understand it much better than we currently do. By and large, the typical evangelical’s understanding of God is pathetically superficial. Too many professing believers think about God in only self-centered and self-indulgent terms, reducing Him to little more than a genie in a lamp. Others are preoccupied with a relational perspective on God. They want Him to be more comfortable and inviting—less of a divine sovereign and more of a casual buddy. Such shallow thinking invites confusion and corruption into the midst of God’s people, and perverts their perspective of their holy Lord and Savior.
In fact, today most of the dominant errors in the church spring from a lack of respect and appreciation for God’s holiness. On the other hand, we can do a lot to inoculate ourselves from bad theology and heresy simply by cultivating a biblical perspective on God’s utterly holy nature.
To begin with, we need to see His holiness as more than just another attribute. A. A. Hodge said,
The holiness of God is not to be conceived of as one attribute among others; it is rather a general term representing the conception of His consummate perfection and total glory. It is His infinite moral perfection crowning His infinite intelligence and power. 
Thomas Watson said, “Holiness is the most sparkling Jewel of his Crown; it’s the Name by which God is known.”  R. L. Dabney wrote,
Holiness, therefore, is to be regarded, not as a distinct attribute, but as the resultant of all God’s moral attributes together. . . . His holiness is the collective and consummate glory of His nature as an infinite, morally pure, active, and intelligent Spirit. 
In Isaiah 57:15, the prophet reports, “For thus says the high and exalted One who lives forever, whose name is Holy.”
God’s being is utterly separate from ours, and Scripture makes that clear. He is being and we are becoming. The Hebrew word for holiness is qadosh; the Greek is hagios. Both have the connotation of something that is distinct and separate. Therefore, nothing in the creation compares to God in His essential nature. He is wholly other than His creatures. He is incomparable. He is infinite perfection. That is why Exodus 15:11 says, “Who is like You, majestic in holiness?” First Samuel 2:2 says, “There is no one holy like the Lord, indeed, there is no one besides You.” The Psalmist says, “Holy and awesome is His name” (Psalm 111:9).
God’s holiness is His otherness. There is nothing, in all of creation, even remotely like Him. The greatest archangel is no closer to divinity than the smallest piece of dust. We must humble ourselves and worship God in recognition of His exclusive, infinite perfections and—in spite of that—His gracious willingness to condescend to us as the beneficiaries of His mercy. To that end, we’ll consider God’s holiness in far greater detail over the days ahead.
Used with permission from John MacArthur.