Q: What is God?
A: God is Spirit, love and light revealed in the person of Jesus and expressed by the Holy Spirit.
God is spirit, and his worshipers must worship in the Spirit and in truth.
Whoever does not love does not know God, because God is love.
God is light; in him there is no darkness at all.
In the beginning was the Word, and the Word was with God, and the Word was God.
Now the Lord is the Spirit, and where the Spirit of the Lord is, there is freedom.
While I think this is a valid question, I don’t think it belongs in a catechism. Catechisms, by nature, seek to provide succinct and memorable answers to concise questions. I don’t think it’s possible to answer this question succinctly and completely. Summing up the Divine Being in a pithy sentence or two of finite human language just isn’t possible. Instead, this question seems to be better suited for prolonged meditation over the course of a lifetime. Sure, there are Scriptures (like the ones I’ve referenced) which provide an adjective or an appositive to describe God, but all of them together are still inadequate. After all, how can finite language hope to fully express the infinite? Doesn’t the Incarnation suggest that God found language alone inadequate to express Himself?