Answer: God is a Spirit₁, in and of himself infinite in being₂, glory₃, blessedness₄, and perfection₅; all-sufficient₆, eternal₇, unchangeable₈, incomprehensible₉, everywhere present₁₀, almighty₁₁, knowing all things₁₂, most wise₁₃, most holy₁₄, most just₁₅, most merciful and gracious, long-suffering, and abundant in goodness and truth₁₆.

1. John 4:24
2. Exodus 3:14; Job 11:7-9
3. Acts 7:2
4. 1 Timothy 6:15
5. Matthew 5:48
6. Genesis 17:1
7. Psalm 90:2
8. Malachi 3:6; James 1:17
9. 1 Kings 8:27
10. Psalm 139:1-13
11. Revelation 4:8
12. Hebrews 4:13; Psalm 147:5
13. Romans 16:27
14. Isaiah 6:3; Revelation 15:4
15. Deuteronomy 32:4
16. Exodus 34:6

For further study see:

1. The story of how Puritan Divine George Gillespie answered the question “What is God?”
2. WSC 4: “What is God?”
3. Dr. R.C.Sproul explains the aseity of God (i.e God’s eternality and self-existence)