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, and the catechism answers with the opening line of Article I of the Confession of Faith: "We believe in the one true, holy and living God, Eternal Spirit." The catechism adds the name Article I reaches in its final sentence, the Holy Trinity, and so gathers the whole article into one line.
The one true God is the confession of Israel: "Hear, O Israel: the LORD our God, the LORD is one" (Deuteronomy 6:4). Jeremiah sets the same confession against the idols of the nations: "the LORD is the true God; he is the living God and an everlasting King" (Jeremiah 10:10). Jesus prays the same way on the night of his arrest, addressing his Father as "the only true God" and binding eternal life to knowing him (John 17:3). Holy comes from the command given to Israel at Sinai: "You shall be holy, for I the LORD your God am holy" (Leviticus 19:2). God's holiness is the reason his people are called to holiness of heart and life, the phrase Wesley used for the goal of the Christian life. Living means that God acts, speaks, judges, and saves; Hebrews asks (Hebrews 9:14).
The Eternal Spirit is the phrase the Confession uses for God's own nature, and Hebrews 9:14 uses it for the Spirit through whom Christ offered himself. God is spirit, without beginning or end, and no part of his own creation. The Holy Trinity is the name the church gives to the one God as he has made himself known, and the catechism cites the baptismal command as its warrant: "baptizing them in the name of the Father and of the Son and of the Holy Spirit" (Matthew 28:19). The name is singular, and 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 is addressed to the living God of Jeremiah 10:10. To know this God, in the words of John 17:3, is eternal life, and the rest of the catechism unfolds what that knowledge contains.