In the most general sense, a theist is a person who believes in at least one god or deity. Theism stands in contrast with atheism (the denial of the existence of any god) and agnosticism (the belief that the existence of a God or gods is uncertain). Theism can include any of the following worldviews:
Monotheism: A monotheist is a person who believes in one God. Monotheism is accepted by Judaism, Christianity, and Islam, although each religion has a distinct view of God.
Polytheism: A polytheist believes in more than one god. Those who believed in the gods of the Greco-Roman culture were polytheists. Today, those who accept the many gods and goddesses of the spirit world would be considered polytheists.
Deism: Deists believe in a God (or sometimes gods) who created the universe but does not operate within the universe.
Pantheism / Panentheism: Pantheists and panentheists believe god is all and all is god. Panentheism also includes the idea that a god or gods created the material universe.
Autotheism: An autotheist is anyone who makes the claim that he or she is God or an enlightened one.
According to Scripture, there is one God who created the heavens and the earth (Genesis 1:1). This teaching is not debated but assumed in the Bible. In fact, Psalm 14:1 teaches, “The fool says in his heart, ‘There is no God.’” Further, the Old Testament clearly teaches monotheism: “Hear, O Israel: The LORD our God, the LORD is one” (Deuteronomy 6:4). Deuteronomy 4:39 adds, “The Lord is God in heaven above and on the earth beneath; there is no other.”
According to the New Testament, God exists as one Triune God comprising God the Father, God the Son, and God the Holy Spirit (Matthew 28:19—“in the name”, singular). All three Persons of the Triune God are also mentioned at Jesus’ baptism, when the voice of God the Father speaks from the sky to Jesus and the Spirit descends like a dove (Matthew 3:16–17).
A Christian is a theist of a particular kind. A Christian is a monotheist who accepts the view of a Triune God and believes in Jesus as the risen Lord (Romans 10:9).