In early form of computer gaming, there was sometimes a 'knights & knaves' scenario, where an adventurer was faced with one person who always tells the truth, and another person who always lies. You were also faced with two choices, one door leads to freedom, the other leads to certain death. Both of the pair knows which door is which, your problem is, you have no idea whom to trust. This simple 'logical' problem was first proposed by Raymond Smullyan, and the resolution of the problem is to ask one of the pair "What would the other person say if I asked him which is the door to freedom?", and take the opposite door. (work it out)
I am not suggesting that the Jacob/MiB scenario is as simple as this, but we certainly have a "we have no idea which one should be trusted" scenario. It has appeared from time to time that both have schemed, plotted and manipulated for their own ends and motives (whether these are good or bad is immaterial at this point). Jacob may or may not have lied, but he has certainly been 'economical with the truth' at various points. We certainly know that MiB told Richard that Jacob was the devil, and the island was Hell; he has also been 'economical with the truth' about Desmond; he told Zoe: "I don't know what you are talking about"; he told Claire that the Others has Aaron.
My point about all this, is that the writers have 'deliberately' developed a knaves & knights-type situation here, but one which cannot be resolved as easily as asking MiB 'What would Jacob say if we asked him?' This is a much more sophisticated, more realistic interpretation of the scenario, where you cannot actually trust either side implicitly. Just to ram home this point, is there anyone willing to lay odds of their $1M to my $1 to bet that Jacob is actually the good guy? I know it's likely, but the story could yet twist and turn so that MiB is the good guy, and Jacob has been the bad guy all along...
Given that, what should we then make of the things claimed to be true by MiB
- The island is Hell
- Richard is the devil
- He is the black smoke
- He can't travel over water
- He masqueraded as Christian
Which ones should we believe, and which ones should we ignore? We can only make sense of the MiB's claims if we know what his actual motives and intentions have been throughout the series, as well as those of Jacob and/or any other island power. Unfortunately, since at this stage we have no idea who is the knave, who is the knight, any attempt to ascribe motives can only be based assumptions about their behaviour and on the things they have said. However, if their actions and statements cannot be trusted, because we do not know which of them (if either) is telling the truth, how can we even get started in this process?
My point about all this, is that the writers have been exceptionally clever so far in leaving certain questions open. Having the MiB tell Jack that he was acting as his father, simply reinforces the 'openness' question. If MiB is the bad guy has a lot to gain by convincing Jack that he understands his father, and has been his 'friend' in the past, and therefore claiming to be Christian is an obvious ploy. If MiB is the good guy, he is simply being honest about the fact that he took Christian's form in order to help Jack at that point. As Mandy Rice Davies once (nearly) said, "Well, he would say that wouldn't he?"
Standing back from all this, you can hear the chuckles of D & C as they witness all the fans arguing with one another about why people are 'still' not accepting that MiB=Christian. The reason there has been so much heated discussion is that it was blindingly obvious we were supposed to think that MiB was Christian. To have set up all this complex scenario, only to throw it away as a simple 'off the cuff' answer seems to me pretty out of character for the writers. I daresay we will hear more about this, but there is a possibility that we won't. It may be that the writers remain deliberately silent on this matter, and leave it as one of those unsolved mysteries that fans will argue over for the rest of time.
However, let me finish by offering you this scenario: At work, there is a guy who always comes in late, dishevelled and dirty; he gives peculiar and spectacularly unconvincing stories about his lateness; he also tels you stories of his private life that you are convinced are completely fabrications. He tells you for example that he went on holiday to Las Vegas, and gives you detals of who he met there, and what he did, when you know for a fact that he was at home in his house. One day out of the blue, some money goes missing out of your desk drawer. There is a big investigation. During this he comes to you to tell you that he stole it. Do you believe him?