The ESV Study Bible is our bible of choice. To show you how good the notes are, we’re sharing pieces from the ESV Study Bible's article on the Trinity.

Four Essential Affirmations

The biblical teaching on the Trinity embodies four essential affirmations:

1. There is one and only one true and living God.
2. This one God eternally exists in three persons—God the Father, God the Son, and God the Holy Spirit.
3. These three persons are completely equal in attributes, each with the same divine nature.
4. While each person is fully and completely God, the persons are not identical.

The differences among Father, Son, and Holy Spirit are found in the way they relate to one another and the role each plays in accomplishing their unified purpose. The unity of nature and distinction of persons of the Trinity is helpfully illustrated in the diagram below.

God Is One God: Monotheism

There is nothing more fundamental to biblical theology than monotheism (the biblical belief that there is one and only one God): “Hear, O Israel: the Lord our God, the Lord is one” (Deut. 6:4). This verse, known as the Shema in Hebrew (from the opening verb of the verse, meaning “hear” or “listen”), is one of the most familiar and foundational verses in the OT. God rejects polytheism (belief in many gods) and demands exclusive devotion: “I am the Lord, and there is no other, besides me there is no God” (Isa. 45:5; cf. Deut. 4:35, 39; 1 Kings 8:60; Isa. 40:18; 46:9). The NT affirms the deity of the Father, Son, and Holy Spirit, as we shall see, but does not waver from OT monotheism (John 17:3; 1 Cor. 8:4–6; 1 Tim. 2:5; James 2:19). Jesus quotes the Shema in a debate with the Jewish leaders (Mark 12:29), and Paul continues to teach that there is one God while recognizing Jesus as the divine-human Mediator between God and man (1 Tim. 2:5).

Implications of Monotheism

Because there is only one God, idolatry of any kind is evil, foolish, wrong, and harmful. Worship of other “gods” robs the true God of the devotion and glory he alone deserves. Idolatry can take many forms. Idols are not only man-made objects but are anything allowed to compete with God for ultimate loyalty. According to Jesus, money can become an idol: “You cannot serve God and money” (Matt. 6:24). Greed, lust, and impurity can also become indicators of idolatry (Eph. 5:5; Col. 3:5). Idolatry is foolish, deceptive, and dangerous—and may even involve demonic activity (1 Cor. 10:19–20). Because there is only one God, he alone should be the ultimate object of the believer’s affections. He alone deserves absolute allegiance and obedience. The Great Commandment that follows the Shema is the obvious implication of monotheism: “You shall love the Lord your God with all your heart and with all your soul and with all your might” (Deut. 6:5). The one true God deserves all we are and have. He deserves wholehearted love because nothing compares with him. To be continued. Taken from the ESV Study Bible. Used by permission of Crossway Books, a publishing ministry of Good News Publishers, Wheaton, Il 60187, www.crossway.org.