Hello!

The verification of memebers was actually just a bit of routine, clerical minutiae-- it was merely a "roll-call" to verify who was in attendance from each delegation, and to verify that this was indeed the person expected based upon election results. It was a benign procedure for what it was: checking that yes, you are Maximilien Robespierre and that you were indeed elected from Arras, and you are a member of the Third Estate. Onto the next.

However because it's the French Revolution we crank everything up to 11 and make it far more exciting than that!

But first a little background is necessary to understand the context. The last Estates General had been convened back in 1614. Due to this last meeting being in the misty past (for reference the span was 175 years. Going back 175 years from today would but us before the Revolutions of 1848, let alone the Civil War in the United States) there was talk that perhaps they should spruce up the rules a bit. The traditional Estates General was a meeting of the Three Estates: the Clergy, the Nobility, and the Everyone-elsers (more realistically upper middle class). The way this body worked was that an equal number of delegates were elected to each Estate, and then votes were taken by Order; in other words each Estate got one vote. Sounds equal, right?

Well the problem was this "equality" was undermined by the fact that the Third Estate represented somewhere around 97% of the population of France, whereas the Nobility and the Clergy comprised that leftover 3%. What made the Vote by Order particularly egregious was that the Clergymen who were elected to the First Estate, usually bishops, abbots, and other high-rung church officials, were almost uniformly from noble families. This meant that the First and Second Estate in essence comprised a voting block, as it would have been rare to see an issue that they didn't agree on. Therefore the Third Estate not only had a tiny percentage of delegates representing most of the nation, but they also were forever going to be outvoted by the other two orders.

So fast-forward to 1788. A popular call had gone around to "Double the Third and Vote by Head!" This rallying cry aimed to effect two changes in the upcoming Estates General. First, they wanted to double the representation of the Third Estate. As in, if the First Estate and Second Estate got to elect 50 dudes apiece, than the Third Estate would then get to elect 100. The second call was arguably the more important of the two, and that was a Vote by Head rather than by Order. This would be critical, for even if the Third's representation was doubled (as it was officially by the monarchy ahead of elections) if the Vote by Head wasn't secured than you'd just have more guys pissed off when their singular Order vote was shot down by the other two Orders. Critically, Louis's ministry failed to make a decision on the Vote by Head / Vote by Order debate even as the Estates General got under way. We can't be certain of motives, but it appears as if by not making a decision, Louis was hoping to foist that decision upon someone else-- or even better upon the Estates General itself. This was a fatal miscalculation, and probably one of the biggest blunders of the Revolution.

Okay now that we've got the necessary background, let's kick off the Estates General, cosplaying as a member of the Third Estate:

We have a dilemma. The King sanctioned the doubling of the Third, but the ministry has not yet made a decision on Voting by Order, or Voting by Head. It's been hinted that perhaps a combination of the two would work, but we know what will happen: if we convenve as the 'traditional' Estates General then the first two Estates will just charge forward, outmaneuvering us and overruling us at every turn.

It's our first official day in the Estates General (yesterday was a procession and some boring speeches), and the first piece of business given to us is to break up into separate orders and verify credentials (i.e. read down the list of names, have delegates submit proof of who they were, etc.). This was a task that has traditionally been done by Order, and so the First and Second Estates have made their way off into their own rooms to verify credentials separately. However, we, the Third Estate delegates, have a plan. In separate verification of credentials we see a big hairy rat. The moment we verify ourselves separately, we fear the "Vote by Head" movement will be all over. Business would continually be done by Order, and nothing will change.

Instead, our Third Estate leadership has put it around that instead of verifying by order, we will insist on verification by head. The roll-call should be done in a large room by everyone as a body-- not as separate orders. We will be clear that until this was done, we will inact no business. We have now turned the "verification of credentials" from a boring clerical task to, arguably, the start of the Revolution.

So it was that the Third Estate's delegates decided from Day One that they would conduct no official business until the Estates General met as a body to verify credentials. Of course the First and Second Estates carried on and ignored this call, but as the days and weeks wore on it became clear that action needed to happen, and eventually the walls started to crumble. A delegation of First Estate delegates came to join the self-styled "National Assembly", followed by a group of liberal nobles. Eventually the King would order all those who hadn't joined the National Assembly to do so, effectively sanctioning the Vote by Head-- way, way, too late. After the Revolution had already begun.

The importance of the move-- to forgo verification of credentials as separate orders-- cannot be understated. There is plenty more here that I didn't touch on due to the massive breadth of the subject, but I hope this answered and expanded upon your initial question! Let me know if you have further questions.