The words "the" and "a" are adjectives. They are used to help define the noun they are describing. When we say, "The boat was caught in a storm," we believe that our audience knows of which boat we are speaking. By simply changing the word "the" to "a," the word "boat" no longer refers to a specific boat, but we could be speaking of a literal boat of the entire category of things known as boats, or a hypothetical boat. Adding other adjectives between "the" or "a" and the noun does not alter the meaning. Suppose you said, "The large, red boat was caught in a storm." You would be assuming that your listeners knew which large, red boat. If you said, "A large, red boat was caught in a storm," you would be informing them that one of many large, red boats or a hypothetical boat matching that description was in danger.
Christianity has been criticized for many things, but the most often heard sentiment is that Christians think they "own God." What the critics are saying is that Christians believe that only their understanding of God is accurate; that all other views are a form of idolatry. Before I address their criticism, let me say that all religions, cults, and atheists believe they know the truth about God. The fact that people disagree with the Christian view of God demonstrates that they have an alternative view. By challenging the Christian view, they are guilty of the same thing for which they so vehemently judge Christians.
The old joke about heaven being divided into sections by walls that isolate each religion from the others so that they can continue to believe they are the only ones there, is funny, but it is definitely impossible. The Bible teaches that there is only one God. "Hear, O Israel: The LORD our God is one LORD" (Deut. 6:4). In Ephesians, Paul writes, "One God and Father of all, Who is above all, and through all, and in you all" (Eph. 4:6). Just a note of caution to my readers: this is written to Christians. Christians are indwelt by God, the Holy Spirit (Jn. 14:17). Notice that the Bible does not say "a God," but "the God" (2 Cor. 11:31; Eph. 1:3; 1 Pet. 1:3).
There is only one way by which man can get to heaven, and that is by faith in Jesus Christ. Jesus said, "I am the way, the truth, and the life; no man cometh unto the Father but by Me" (Jn. 14:6). There is only one thing that God requires of man, and that is to "believe on Him (Jesus) Whom He hath sent" (Jn. 6:29). God does not say, "Believe in Me." He says, "Believe on Jesus!" The word "on" implies to place one's trust in, or count upon Him. Christianity is the belief in the God, and the way to the God, Jesus Christ.