Nothing seems to have tempted early man much more than a desire to worship false gods and idols. Idolatry was rampant during the Patriarchal age and became so among the Israelites under the Mosaical dispensation, even after the extremely strong warnings from God concerning that. When He gave Moses the ten commandments engraved in stone, it is worthy of note that the article title above was the very first of the ten. Here is what He said in its entirety and please take note of the fact that He acknowledges that He is a jealous God
"Thou shalt have no other gods before me. Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth: Thou shalt not bow down thyself to them, nor serve them: for I the LORD thy God am a jealous God, visiting the iniquity of the fathers upon the children unto the third and fourth generation of them that hate me; And shewing mercy unto thousands of them that love me, and keep my commandments." (Exodus 20:3-6 KJV)
When this commandment is considered in its proper relationship, it is very easily understood why God would, not only desire, but would expect, His creatures to place him in the highest position of respect and reverence. After all, He created the universe and he created man. All things are His. To worship some inanimate object or some solar body which has no mentality and no power to create or aid one, is folly and certainly insulting to the omnipotent Father of the universe and all that is in it.
Jesus proclaimed, when tempted by Satan, "Thou shalt worship the Lord thy God, and him only shalt thou serve." And this statement is recorded both by Matthew and Luke.
As many other things are so described in the Bible, there are no other Gods. Let us examine the things which are mentioned as being the only one for its position or cause.
In John 14:6, Jesus lets us know that he is the only way that one may get to heaven. "Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me."
And Jesus, as did God in the first commandment, had ample reason to make that claim. Prior to his sinless life and his sacrifice on the cruel cross, there was no way for man to rid himself of sin. Even those who had kept the Mosaical Law well, still had every one of their sins to account for, until Jesus died for them, just as he did for us. Their law only allowed for them to roll their sins forward for one year and they were then remembered against them. But Jesus' sacrifice forgave them to be remembered no more.
Paul, in his letter to the Ephesians let them all know that the church's foundation was lain by the apostles and prophets but that no other than Jesus was the chief cornerstone. "...having been built on the foundation of the apostles and prophets, Jesus Christ Himself being the chief cornerstone." (Ephesians 2:20 KJV)
Jesus foretold to the apostles that his church (kingdom) would be built on the rock of truth that he was the Son of the living God. Read Matthew 16:13-20
We find in Acts 4:12, that there is salvation in no other name, than Jesus'. "Neither is there salvation in any other: for there is none other name under heaven given among men, whereby we must be saved."
And Paul, in his letter to the Galatians lets us know that there is no other gospel, than that of Jesus Christ, that which is in the New Testament, which will be acceptable: "But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. " (Galatians1:8 KJV)
The scripture above, includes every instruction which is not included in the New Testament is invalid, even if they claim that the Bible has been distorted or that further instructions were forthcoming from some angel. All those are to be accursed.