The point was that there was a very obvious way for Brian to escape: he could pretend to be a carpenter.
But he didn't. Monty Python chose the less obvious way for Brian to escape. That was the joke.
I think it should simply be edited out. Terry Jones admitted it was a
deus ex machina, inspired by the success of Star Wars at the time. If they had to have an impossible scape, they decided to have a "totally ludicrious" one.
They should have used those 3 minutes to put the Otto sketch in:
[Otto] - Hail, leader.
[Brian] - What?!
- Oh, I'm so sorry, Have you seen the new leader? I wish to find him and hail him.
- Who are you?
- My name is Otto.
- Oh, Otto... Well, I'not sure -
- Oh, I grow so impatient, you know, to see the leader that has been promised our people for so many centuries, the leader who will save Israel by riding it of the scum of non-jewish people, making it pure, no foreigners, no rifraf, no gypsies....
- Shh, Otto...
- What, the leader? Hail, leader!
- No, no, it's dangerous...
- Dangerous? This is no danger. Man! [man march in] Impressive, eh?
- Yes.
- Oh, yes! We are a fairly trained suicide squad.
- Oh.
- Oh, yes. We can commit suicide within 20 seconds.
- 20 seconds?
- You don't believe me?
- Yes!
- I think you question me.
- nonono...
- I can see you do not believe me.
- No no, I do.
[Otto] - Enough. I prove it to you. Squad!
[Squad, chorus] - Hail, leader!
- Commit suicide!
- ...twothree onetwothree onetwothree one... aghhh...
[Otto] - See?
[Brian] - Yes
- I think now you believe me, yes?
- Yes, very impressive.
- I think now I prove it to you, hah?
- Yes.
- All dead. Not one living. He's dead [pointing], and he's dead, see? I thread on him. And he's dead, and he's dead. They're all dead. All dead good jewish boys no foreigners! But their names will live for ever! Helmut, Johnny, the middle guy... and the other fat one. They're names will live
eventually forever.
[noises among the fallen man]
[Otto] - Wait a minute! There's someone here who is not dead! There's someone here who is only pretending to be dead! Stand up you! [kicks a body] [Ow!] Who said ow? You're not dead either! Neither are you! Stand up, stand up! You're not dead! Oh, my head. Stand up, stand up, all of you. Oh, my head, is not even one dead?!
[soldier, mumbles] - Yes, sir, not one...
- Why not?
- We thought it was a practice, sir.
- But all the bleeding, and the groaning?
- A little secreted sheep's bladders, sir.
- Oh, my cock! Sheep's bladders?! You are sour, a non-semitic mutinous racially impure clotied bunch of roman lovers! Tomorrow, as a punishment, you will all eat... pork sausages!
- Oh, no...
[Otto] - All right, tell the leader we are ready to die for him the moment ze gives the sign.
[Brian] - What sign?
- The sign that is the sign. That shall be the sign. Man!... fooorward!
[Squad, chorus]
There's a man we call our leader,
He's fine and strong and brave.
and we follow him unquestioning,
towards an early grave.
He gives us hope of sacrifice,
and a chance to die in vain.
And if we are one of the lucky ones,
we will live to die again!
[Brian] - Silly bugger!