You are correct in thinking that the Bible is intended to be a rich source of spiritual support and understanding. It’s sad that so many people feel the need to use it as a kind of religious weapon, to justify their own attitudes and attack others whose beliefs are different. The Pharisees of Jesus’ day were also fond of the same kind of literal, absolutist reading of scripture—and Jesus took every opportunity to challenge them on it. He certainly knew scripture as well as them, but he also knew that we are here to grow in spiritual awareness—not to mindlessly repeat the attitudes of the past.
The passage from Revelation 3:15-16 (RSV) reads: "I know your works; you are neither cold nor hot. Would that you were cold or hot! So because you are lukewarm, and neither cold nor hot, I will spew you out of my mouth." The speaker is the Christ—"the son of man"—who has appeared in a vision to John and is dictating letters to seven early Christian churches. Metaphysically, these letters serve as wake up calls to the spiritual powers within us that need to be energized—awakened—if we are to accomplish our spiritual purpose. The meaning here is that we can’t be lukewarm about our commitment to that spiritual purpose—we can’t try to balance our mortal needs and our spiritual purpose. It’s only by surrendering completely to the Presence of God within us that we can allow that Presence to provide whatever balance we may need. "Seek first the kingdom of God and its righteousness," Jesus taught, "and all things else will be given to you." Jesus also said—repeatedly—"Judge not." Nothing in this passage—or in the Bible as a whole—gives anyone the right to pass judgment on anyone else’s path, process or beliefs.