God has revealed himself as the God who is. He is the eternal being, existing in an eternal present. His unique, self-identifying name is I AM.
When Moses asked him what his name was he said: 'I AM WHO I AM. This is what you are to say to the Israelites: 'I AM has sent me to you.' [Exodus 3:13-15].
In naming himself this way God teaches us that he has no beginning and no ending. He is, in fact, the beginning and the ending, the source and the goal, of everything else that exists [Romans 11:36; 1 Corinthians 8:6; Clossians 1:16; Revelation 1:8,17; 2:8].
We must also include in this the concept of God's infinity. He is the one who cannot be measured, who cannot be compared or likened to anything else that exists. He simply is. Infinite. Immeasurable. Limitless. Incomparable. [Isaiah 40:12-26].
God also reveals to us in this self-identifying name that he is constant and unchangeable. He is the 'same yesterday, today and forever' [Malachi 3:6; Hebrews 13:8].
When Jesus Christ, the eternal Son of God, walked on this earth, he claimed for himself this same unique name, and by referring to himself in this way clearly identified himself as God [John 8:24,58]. Here in the incarnation the One who is beyond comprehension made himself known: the eternal One bound himself within created time; the infinite One bound himself within created space; the incomparable One bound himself to human flesh and becoming one of us called us 'brothers' [Hebrews 2:11,12]. Here the One who is unknowable became known [John 1:18; 14:7-9].
With such a God as this, who transcends the limits and boundaries of both time and space, we can live in the limitations of time and space with great confidence and assurance. This is our confidence: that wherever we are, God is there, no matter what the time, God is there [Psalm 139:1-18], and, irrespective of our own changeability and the fickleness and transience of everything else that we experience, God does not change.
[This name 'I AM' is the name 'Jehovah', 'Yahweh', or LORD in English usage.]