Sometimes Christians are misunderstood and thought to believe in three gods instead of one. This is because of their belief in the Trinity or triunity of God. If you want to know what Christians believe, it is best to ask Christians, not someone else. That is true of understanding anyone's beliefs. Christians do not believe in three gods. The Bible teaches that there is only one true and living God.
“For there is one God, and one mediator between God and men, the man Christ Jesus;” 1 Timothy 2:5
“... We know that an idol is nothing in the world, and that there is none other God but one.” 1 Corinthians 8:4
The Bible also teaches that God is a Trinity, that is, that He exists in three distinct persons: Father, Son and Holy Spirit.
“Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:” Matthew 28:19
Even though the word "Trinity" is not found in the Bible, the doctrine is taught. The word "Bible" is not found in the Bible either, but I understand from reading the Bible that God is a Trinity, that is, He is one God in three persons.
JESUS IS GOD:
“And after eight days again his disciples were within, and Thomas with them: then came Jesus, the doors being shut, and stood in the midst, and said, Peace be unto you. Then saith he to Thomas, Reach hither thy finger, and behold my hands; and reach hither thy hand, and thrust it into my side: and be not faithless, but believing. And Thomas answered and said unto him, My Lord and my God. Jesus saith unto him, Thomas, because thou hast seen me, thou hast believed: blessed are they that have not seen, and yet have believed.” John 20:26-29
THE HOLY SPIRIT IS GOD:
“But a certain man named Ananias, with Sapphira his wife, sold a possession, And kept back part of the price, his wife also being privy to it, and brought a certain part, and laid it at the apostles’ feet. But Peter said, Ananias, why hath Satan filled thine heart to lie to the Holy Ghost, and to keep back part of the price of the land? Whiles it remained, was it not thine own? and after it was sold, was it not in thine own power? why hast thou conceived this thing in thine heart? thou hast not lied unto men, but unto God.” Acts 5:1-4
THE FATHER IS GOD:
“But to us there is but one God, the Father, of whom are all things, and we in him; and one Lord Jesus Christ, by whom are all things, and we by him.” 1 Corinthians 8:6
Even though the Father, Son, and Holy Ghost are all three God, there is only one God. An easy way to understand this concept is by using the idea of H2O. H2O is the formula for water, ice and steam. Water, ice and steam are all H2O, yet they are distinct. One is solid. One is liquid. One is vapor. Yet, all are one substance: H2O.
God is Father, Son and Holy Spirit, yet He is one.
“For there are three that bear record in heaven, the Father, the Word, (another name for Jesus Christ) and the Holy Ghost: and these three are one.” 1 John 5:7
It is thought by many scholars that the verse we just quoted, 1 John 5:7, was not originally a part of the Bible, but was added later. While we disagree with this view, (here's why) the fact that this verse appears in the Bible, and the fact that it is quoted in Christian writings from the 4th and 5th centuries A.D. shows that early Christians believed the doctrine of the Trinity. Early Christian creeds and confessions also state a belief in one God who exists in three eternal persons. Christians understood this and believed it from ancient times because the Bible clearly teaches it.
The plain Bible teaching that there is only one God, when compared with the equally clear teaching that Jesus, the Father and the Spirit are God, leads us; and has lead Christians for nearly two-thousand years, to the logical conclusion that God is a Trinity.