How Denying Deity Changes the Gospel

Questions about why it’s necessary to believe Jesus is God, whether belief in the Trinity is required for salvation, and why one has to believe in the Trinity if the words “Trinity,” “God the Son,” and “God the Holy Spirit” aren’t in the Bible.  

• Why is it necessary to believe Jesus is God? Since the Trinity is so difficult for our little human minds to comprehend, is belief in the Trinity really required for salvation?
• Where do you see the words “Trinity,” “God the Son,” and “God the Holy Spirit” in the Bible, and if they’re not there, do I have to believe in the Trinity?