Who is God?
God is the one true, holy and living God, the Eternal Spirit, the Holy Trinity.
Catechism for the Global Methodist Church, question 2
4Hear, O Israel: the LORD our God, the LORD is one.
2Speak to all the congregation of the sons of Israel and say to them: You shall be holy, for I the LORD your God am holy.
10But the LORD is the true God; he is the living God and an everlasting King; at his wrath the earth quakes, and the nations cannot endure his indignation.
19Therefore go and make disciples, baptizing them in the name of the Father and of the Son and of the Holy Spirit.
3This is eternal life, that they may know you, the only true God, and the one you sent, Jesus Christ.
14how much more will the blood of Christ, who through the eternal Spirit offered himself without blemish to God, cleanse our conscience from dead works so that we may serve the living God.
The first question asked for a profession of faith. This one asks who the God of that profession is. The words come from Article I of the Confession of Faith, which opens, "We believe in the one true, holy and living God, Eternal Spirit," and closes with the name Holy Trinity, so the whole article stands behind this one line.
God is one, and there is no other. Israel confessed this every day: "Hear, O Israel: the LORD our God, the LORD is one" (Deuteronomy 6:4). God is true, and the idols of the nations are false; Jeremiah wrote against them, "the LORD is the true God; he is the living God and an everlasting King" (Jeremiah 10:10). On the night of his arrest Jesus prayed to his Father as "the only true God" and said that eternal life is to know him (John 17:3). God is holy, and because he is holy his people are called to be holy: "You shall be holy, for I the LORD your God am holy" (Leviticus 19:2). Wesley called this holiness of heart and life, and it is the goal of the Christian life. God is living: he acts, speaks, judges, and saves. Hebrews asks (Hebrews 9:14).
God is the Eternal Spirit. He has no body, no beginning, and no end, and he is no part of his own creation. The Confession uses the phrase for God's own nature, and Hebrews 9:14 uses it for the Spirit through whom Christ offered himself. God is the Holy Trinity, the one God as he has made himself known: Father, Son, and Holy Spirit. Jesus commanded baptism in this name, "baptizing them in the name of the Father and of the Son and of the Holy Spirit" (Matthew 28:19). The name is singular; the persons are three.
For a Methodist this answer is the ground of worship. Every baptism in the church is performed in the threefold name of Matthew 28:19, and Sunday praise goes to the living God of Jeremiah 10:10. To know this God is eternal life, as Jesus said in John 17:3, and the rest of the catechism teaches what that knowledge contains.