The purpose of this post is 1. (to get away from Romans for a wee bit) and 2. to counter a classic approach to these two words 'hot' and 'cold.'
The classic approach, like I have seen preached, and I'm sure many of you may have seen preached, is it is worse to be middle-of-the-road complacent in your spiritual life and faith, than it is to be hostile to faith. -or- it is better not to know Christ than to be only half-passionate about him. -or- more strongly still, being heretical/anti-gospel is just as good as being on-fire passionate for God in being better than knowing the gospel, but being half-hearted or lukewarm or nearly warm or nearly passionate about it.
This does seem a wee bit odd doesn't it? I think the problem comes primarily from misunderstanding the word 'cold' - and to understand it properly we need to look to extra-biblical sources.
We learn that Laodicea was located nearby Colossae and Hierapolis. Hierapolis was located in and around mineral hot-springs, so had an abundant and well known supply of hot water. This was used in part for bathing in, to heal joints and ligaments, and sweat out impurities in the skin, this included killing germs and bacteria’s. In short, Hot water in nearby Hierapolis was known for its healing properties. Colossae at the other extreme was located in the highlands with pools of refreshing (and very very cold!) water. This was wonderfully refreshing to drink and helped supplement a good diet, healthy life style and alertness/vigour of its drinkers. Laodicea however, being placed on trade routes rather than near natural supplies, piped its waters from Hierapolis. Once this water had arrived it had cooled somewhat to become lukewarm. Lukewarm water lacks the healing properties of hot water, and the refreshing qualities of cold, instead it is good for only one thing: as an emetic (an agent that causes vomiting). Such water is putrid, nauseating, and above all, pretty useless.
The Laodiceans are addressed from the faithful witness. We learn from the other six letters in the beginning of Revelation, that the titles Jesus addresses himself with act as an important prologue/link to the main issues of the receiving church. The Laodiceans thought they had everything they needed; they made themselves rich and content apart from Christ. This makes the Church at Laodicea with this attitude to be little better than a secular pagan institution, one without place in Christ's kingdom, or on his throne (vv. 21-22), so are to be spewed out of his mouth. As a secular institution they are not delighting in the gospel and they are not faithfully witnessing to outsiders. Making them useless (Lukewarm).
Hot and Cold are both positives, they heal and refresh. They take delight in God's kingdom and they spread the gospel. Lukewarm is complacency and uselessness, missing the life-changing delights of being in God's kingdom, and being so worldly loosing the importance of witness.
Jesus is not saying in this letter that it is better to be anti-gospel or heretical than middle-of-the-road, or not always totally passionate in your faith. He is saying, however, that one must let the gospel affect your life and must use that as a witness to those outside the church.
Lets stop being overly worldly and complacent in our lives, so making ourselves fit to be vomited from the kingdom. But lets keep humbly acknowledging the gospel, keep submitting to it, and seek to see how we can be used in the service of the king - making ourselves, in grace, fit to be further digested into Christ's kingdom.