It's not below the belt at all, and it's not offensive. In fact, many Christians themselves have a hard time wrapping their head around this concept. I can give you a better explanation than you've probably heard till now, and in fact, better than many Christians have heard. Early Christians who were dealing with three supernatural entities (Father, Son, and Holy Spirit) were familiar with two kinds of current theologies: the monotheistic Judaism and the polytheistic Greek or Roman pantheon of gods and goddesses. These Christians developed the three-in-one concept of the Trinity. Basically, while each entity was an individual, they had almost everything in common, were compatible, worked together, were harmonious, etc. That is, in comparison to the polytheistic pantheons, whose individuals often worked against each other, fought each other, stole from each other, bedded each other's women, etc. The pantheon was a cutthroat, every-man-for-himself, battle royal kind of outfit. More pathetic than pantheon, if you ask me. It was like playing rock-paper-scissors at the supernatural level. So that's the Trinity in a nutshell: three individuals, but not to worry, because they're all on the same page, they're all in complete agreement.