Pride is the chief of all sins, as well as the chief cause of all sin. We learn from the prophet Ezekiel that this was the most essential problem with Sodom (16:49-50), and Paul teaches us that this is the sin that brought condemnation on the devil himself (1 Timothy 3:6).
C. S. Lewis identifies the unique place of pride among sins in chapter 8 of Mere Christianity::
According to Christian teachers, the essential vice, the utmost evil, is Pride. Unchastity, anger, greed, drunkenness, and all that, are mere fleabites in comparison: it was through Pride that the devil became the devil: Pride leads to every other vice: it is the complete anti-God state of mind.
As Lewis describes it, pride is an “anti-God” state of mind. It is a state of mind or, more essentially, a condition of the heart in which a person has supplanted the rule of God over their lives with the rule of their own will. Instead of depending entirely on God, as was God’s design, a proud heart now looks to itself to decide what is good and evil (see Genesis 3:4-6).
Most essentially, pride is an attitude of independence from God. It is synonymous in Scripture with being haughty, scoffing, arrogant, foolish, evil, and wicked (Psalm 10:4; Proverbs 8:13; Isaiah 2:11, etc.). It is directly opposed to the humble, God-fearing, meek, lowly, trusting, faith-filled disposition that is pleasing to God; its end is destruction.
For the LORD of hosts has a day against all that is proud and lofty, against all that is lifted up—and it shall be brought low; … the haughtiness of man shall be humbled, and the lofty pride of men shall be brought low, and the LORD alone will be exalted in that day. (Isaiah 2:12, 17)