It's based around the central observation that the sacrifice at the heart of the Christian gospel is essentially kind of illogical, and whilst it doesn't really intend itself to be taken that seriously there are a couple of observations I'd like to share.
Firstly, I'm reminded of the parallels with Spock's sacrificial death in Star Trek: The Wrath of Khan. There, Spock, who I assume would think roughly in the same way as the Terminator, sees the bigger picture and bases his decision, logically, on that. (This is notably different from the Terminator's own self-sacrifice at the end of Terminator 2). Here, however, under a narrower set of orders (to preserve the life of Jesus), Jesus's actions make no sense to him. I guess he's not the first person to struggle with that.
Secondly, the film highlights a theological / humorous point I've seen made elsewhere (by Lee and Herring's Sunday Heroes) about the role of Judas, who, as both films claim, Jesus actually needed to betray him. Lee and Herring are, unsurprisingly, a little more cynical about this. I think, though, that both miss the point. From a historical point of view Jesus died because it was politically expedient for him to. So had Judas not betrayed him, it is highly likely that his opponents would have found a way.
As for the film itself, whilst it was mildly amusing, I'm getting a little weary of popular culture's conviction that stuff like this is utterly hilarious. "Look it's someone in a sheet and a beard NOT being holy". Side-splitting. I guess there's just something in the triteness of films like this that I just feel uncomfortable with (and I say that as someone who's a big fan of Life of Brian - in fact it's probably because I'm a fan of Life of Brian).
For anyone who is interested, there's another Lee and Herring Sunday Heroes episode here, although some may find this offensive.