The Birmingham Yardley MP, Jess Phillips, is known for her plain speaking, and she has a standup comedian’s sense of timing. A clip of her speech on Monday night pouring scorn on the government’s new immigration bill has been viewed getting on for 2 million times – and when James Corden and Gabby Logan are both admiringly tweeting about it, something has gone right.

A speech that makes a great tweet is one thing. But is it a great speech?

It’s a long time since a speech needed to last for at least three hours to achieve greatness. The Gettysburg Address is famously only 272 words, and, at the normal broadcasting speech speed of three words a second, it would have taken Lincoln approximately a minute-and-a-half to deliver. But it hit a whole series of targets – the ambition of the founding fathers for equality and liberty, and the idea of a great national sacrifice to fulfil the ambition of “government by the people, of the people, for the people” – in the simplest and most direct language. A great speech is like a great cartoon. It condenses everything, detail and nuance and fact, to convey the essence of the thing.

Phillips would fall about laughing at the comparison. But her speech deployed exactly those techniques, just modified to suit the speaker and the occasion. It was all the more powerful for coming in a debate during which the Labour leadership’s shameful lack of principle was brutally exposed, as the whips swithered and faffed about whether or not to abstain on a mean and confused measure that risks aggravating the hostility to migrants already stoked by Brexit.

The speech that has gone viral takes issue with the definition of a skilled worker being, for the purposes of the new legislation, someone earning more than £30,000, and scoffs at the idea that high incomes mean high skills: “It’s frankly insulting … to our care workers, our nurses, our teachers … there’s so many people that don’t earn over £30,000. I thought I’d met posh people before I came here, but actually I’d just met people who eat olives … I’ve met lots of people who earn way more than £30,000 who have absolutely no discernible skills … not even one.”

Making other MPs laugh, especially on the opposition benches, is always useful – and it’s most useful of all when, like Phillips, it’s in order to make a really serious point. Most of the time, other MPs don’t even hear what speakers say, let alone respond. Being passionate and sincere, and also funny, is a rare combination. It’s almost unheard of when the debate is about detail of legislation.

But it’s not just MPs who don’t hear what’s said in the Commons. The rest of us don’t either. And this is where social media is turning out to be an unlikely platform for parliamentary effectiveness. Jeremy Corbyn’s team has always understood that. No prime minister’s question time is over until the leader has delivered the soundbite that works as a 15-second clip. The SNP MP Mhairi Black’s maiden speech went viral when she came into the Commons as the most unlikely winner of the 2015 election, having unseated Labour’s campaign manager Douglas Alexander before she was even 21. David Lammy did it last year, on the Windrush scandal.

There’s a common factor between these three: each time, the subject was something they knew at first-hand – they were talking about their constituents and the enormity of Westminster’s failure to understand and respond to their needs.

At Gettysburg, Lincoln may have lifted the spirits of the bereaved whose menfolk were about to be buried. No one thought much of it at the time. But it lived on because it came to give purpose and nobility to the union cause.

Phillips’ speech may not make a difference to the immigration legislation. But its afterlife, like last week’s Twitter sensation, Rutger Bregman – the Dutch historian who told Davos to stop talking about philanthropy and start talking about taxes – indicates how great the hunger is for a government that has the courage to use the power of a compassionate state. A speech that delivers a message with the wit and the authenticity that can tap into social media may have become the new measure of greatness.

Only, as Tommy Robinson supporters demonstrate, going viral on Twitter is no more an indicator of moral worth than earning more than £30,000 is reliable evidence of high-grade skills.

• Anne Perkins is a writer and broadcaster, and former Guardian correspondent