The theologians explain to us the difficulty that implies about saying who is God. Thomas Aquinas theologian and scholastic philosopher teaches us in the Summa Theologiae: "Do not pretend to achieve what you can not", Art 1 Q 1. Thomas Aquinas explains that the sacred science, the study of God is called Theology and that the goal of this science is the eternal happiness: "Sacred science revolves around God, so much so that it is called Theology, which is almost like saying Tractate about God." Art 7 Q 1.
Thomas Aquinas makes a special analysis: "Even when we can not say about what God is, in this sacred doctrine we take its effects, as a substitute for the definition to be able to analyze what in this doctrine is said of God." Art 7 Q 1 (Summa Theologiae). That is, we know God by his effects, that is, by his gifts, "the invisible of God is made comprehensible and visible through the created", Art 2 Q2 (Summa Theologiae).
The Bible affirm: "God is spirit", John 4:24 (A1 Q 3); "Be perfect as your heavenly Father is perfect," Matthew 5:48 (A 1 Q 4); "Let us make man in our image and likeness", Genesis 1:26 (A 3 Q4).
Theology is to say the study of God takes the Bible as revealed truth, that is why St. Augustine and St. Thomas affirm that God is the wisdom itself and that God is the origin of the perfections we observe in creation, we call these perfections gifts. The Kingdom of God is the empire, dominion, reign of the divine perfections, dominion of mercy, perseverance, wisdom. Following this idea the sense of spirituality is to reach the full resemblance to God, that is to say to be "full of the holy spirit" or to express it in another way the equality with saints, angels, archangels and other semidivine beings.
Thomas Aquinas concludes with a metaphor affirming: "The Holy Spirit is love, it will be love of love and spirit of the spirit", Question 37, A 1 (Summa Theologiae).