Summary: The whole Bible expounds upon the holiness of Almighty God. All Bible references are from the NASB.
One man described his observations of the concept of holiness like this: “There is a simple yet profound word which occurs nine hundred times in the Bible. You see it first in Genesis, as we are told how God created heaven and earth. You see it last in the closing chapter of Revelation where we are told about God’s creation of a new heaven and a new earth. But except for a few grand old hymns of the faith, you do not see this word much today … This word is “Holy.” We get our words “saint,” “sanctify,” and “sanctification” from the same root words. All these terms carry the idea of being “set apart.…” Just as all the colors of the spectrum come together to form the pure white light which illuminates our world, so all the attributes of God come together into His holiness. 
This attribute of God, His being holy is important for us to understand. Why? Because of God’s commandment in Leviticus and repeated in NT letter of 1 Peter:
1 Peter 1:14–16 As obedient children, do not be conformed to the former lusts which were yours in your ignorance, 15 but like the Holy One who called you, be holy yourselves also in all your behavior; 16 because it is written, “YOU SHALL BE HOLY, FOR I AM HOLY.”
Herein is our problem today: D.A Carson wrote in his book, “For the Love of God,” the following, “People do not drift toward holiness. Apart from grace-driven effort, people do not gravitate toward godliness, prayer, obedience to Scripture, faith, and delight in the Lord. We drift toward compromise and call it tolerance; we drift toward disobedience and call it freedom; we drift toward superstition and call it faith. We cherish the indiscipline of lost self-control and call it relaxation; we slouch toward prayerlessness and delude ourselves into thinking we have escaped legalism; we slide toward godlessness and convince ourselves we have been liberated.
In our “Read through the Bible” program, if you got nothing else out of the book of Leviticus, get this, we cannot approach a Holy God on our own terms, we cannot approach God just because we want to. We do God no favors by just showing up at church and putting a $10 bill in the offering. God cannot be bought. We must approach a most holy God in humbleness, confessing our sins and in an attitude of repentance. That’s just for starters.
Isaiah found himself in the throne room of God. Let’s read his account of what took place.
Philadelphia pastor James Montgomery Boice once spoke to a discipleship group on the attributes of God. He began by asking them to list God’s qualities in order of importance. They put love first, followed by wisdom, power, mercy, omniscience, and truth. At the end of the list they put holiness. “That did surprise me,” Boice later wrote, “because the Bible refers to God’s holiness more than any other attribute.” The Bible doesn’t generally refer to God as Loving, Loving, Loving! Or Wise, Wise, Wise! Or Omniscient, Omniscient, Omniscient! But over and over we read the cry of the angels, Holy, Holy, Holy! 
This is where Isaiah stood in today’s passage:
Isaiah 6:1 In the year of King Uzziah’s death I saw the Lord sitting on a throne, lofty and exalted, with the train of His robe filling the temple.
We do not know how Isaiah saw God. In a vision? In person? Isaiah, from a royal family, was probably a high court official. Putting things into perspective, King Uzziah (also known as King Azaraiah in 2 Kings) was a good King, reigned 52 years, had good prosperity. But he was prideful - After all he was king and doing good things, he thought he would top it off by burning some incense himself to God, a job for only the priest.
2 Chronicles 26:16 But when he became strong, his heart was so proud that he acted corruptly, and he was unfaithful to the LORD his God, for he entered the temple of the LORD to burn incense on the altar of incense.
The priest demanded he leave but the king refused
2 Chronicles 26:19 But Uzziah, with a censer in his hand for burning incense, was enraged; and while he was enraged with the priests, the leprosy broke out on his forehead before the priests in the house of the LORD, beside the altar of incense.
He was a leper till the day he died.
In Leviticus, the sons of Aaron, Aron being the first priest and his son being priests after him, were struck dead because they chose to do things their own way.
Leviticus 10:1–2 Now Nadab and Abihu, the sons of Aaron, took their respective firepans, and after putting fire in them, placed incense on it and offered strange fire before the LORD, which He had not commanded them. 2 And fire came out from the presence of the LORD and consumed them, and they died before the LORD.