God is an incomprehensible mystery. This concept arises out of the revelation of the personal character of God in the economy of salvation. When Moses asked God his name, God responded to Moses’ request by giving a virtually unpronounceable tetragrammaton. YHWH, a name so scared that only rarely could it be uttered. The name is often translated as “I Am Who I Am,” or “He Who Is,” but it may also be translated as “I will be with you there as Who I Am will be with you.” The name of God, which expresses the essence of God, amounts to a promise to be there always.
God is an incomprehensible mystery. The unfathomable mystery is that God is bound to humanity and its history through an unalterable covenant that was freely initiates out of love and is destined to be upheld despite the sin of the world. For Christians, the incomprehensibility of God takes on a new dimension in Christ: The invisible God is made visible in the humanity of Christ (oikonomia). And yet, God who is completely disclosed in Christ remains nonetheless veiled. An analogy can be drawn with our knowledge of other human persons. We speak of a person revealing herself or himself to us. By that we do not chiefly mean leaning facts about that person’s past or present but seeing with the “eyes of the heart” who that person is, grasping through love her or his ineffable and inexhaustible mystery. The more intimate our knowledge of another, the more we are drawn to that person’s unique mystery and the deeper that mystery becomes. The same is true of God; God is not less mystery on account of God’s radical immanence in Christ. Indeed, the God who is absolutely Other, absolutely Transcendent but also absolutely near to us – this God is absolute mystery.
 Tetragrammaton: The Hebrew name of God transliterated in four letters as YHWH or JHVH and articulated as Yahweh or Jehovah.
 C. M. LaCugna, “The Trinitarian Mystery of God,” in Systematic Theology: p. 151-192 at 156.