For a political party opposition is a difficult, exhausting and an unattractive business. If the purpose of a party is to bring about change in society and shape it to reflect the values of its own ideology, then parliamentary opposition seems the wrong place to be. Opposition is the antithesis of what parties are for. Or so it seemed. Jeremy Corbyn’s refreshed mandate as leader of the opposition has been cast as a triumph of party members over the party’s members of parliament.

The Labour leader’s supporters say their “movement” should be seen as part of a global trend comparable to the grassroots success of US senator Bernie Sanders or the advances of Podemos’s people’s assemblies in Spain. While social movements have a dynamism missing from slow-moving parliamentary processes, it is a mistake to think representative democracy is redundant in an age of networked politics.

The British parliament is the cockpit of the nation’s history. A functioning opposition is not merely sufficient, it is necessary to provide serious scrutiny of government legislation, especially when such a prospectus is unapproved by the electorate. As the sage of parliament Walter Bagehot noted, this country was the first that “made a criticism of the administration as much a part of the polity as administration itself”.

However integral the role is, parties do not seek opposition. They have it thrust upon them. Of course, losing an election might mean a party has time to reflect, renew and reinvigorate itself. MPs in opposition have to show that the policies and positions of the victorious party are damaging and wrong. Close, patient arguments can secure concessions from ministers that lead to real change in policy.

That is why the relationship between Mr Corbyn and the party he leads is so important. Labour needs to come together, not come apart. Some of Mr Corbyn’s more hardline supporters see the scale of his victory as a licence to expunge internal dissent. In this view, the renewed mandate from members must be deployed with force to refashion the party machine and its parliamentary representation to better reflect the leader’s agenda. There will be pressure on nay-sayers to change their tune or quit.

But the rebels are already chastened. Owen Smith’s challenge failed. Those Labour MPs who expressed no confidence in their leader have no choice but to accept that their judgment has been overruled. They might not be able to change their opinion but they should be constructive and discreet with criticism. The running commentary on Mr Corbyn’s performance from his own benches must stop. Likewise, the talk of punitive deselection for non-compliant MPs should be dropped. Labour has wasted the summer arguing with itself. That is not Mr Corbyn’s fault – he was responding to an internal challenge. But it has, perversely, suited him. He has proved his strength in the small arena of party opinion, thus deferring the challenge of persuading the much wider audience that decides general elections.

His parliamentary enemies have obstructed his leadership, yet some of his supporters have come to rely on that obstruction to sustain the feeling that victory is available. A local enemy within the left is easier to fight – and much easier to beat – than a distant Tory government that hardly feels the need to engage in combat with Mr Corbyn at all.

The parliamentary rebellion has neither the strength nor the authority to prosecute continuing war against the leader, and to try would be futile. Mr Corbyn has won. Twice. Labour’s platform will necessarily become more Corbynite. But what exactly does that mean? His supporters believe he embodies a set of values that they want the party to represent. That is a mostly abstract proposition, made concrete in a handful of emblematic policies – nationalising the railways; opposing grammar schools. During the leadership contest, Mr Corbyn rarely came under pressure to develop his agenda beyond bullet points. It was sufficient to assert the ideal, without explaining how it is realised. That vagueness is a luxury he can no longer afford. After the railways, what else might Labour bring into public ownership? If Labour opposes grammar schools and mistrusts academies, would Mr Corbyn shut down the ones that exist already? With what would he replace them? Every assertion of principle begets multiple questions of practice.

Unsupportive Labour MPs never stopped Mr Corbyn from giving answers before and are not stopping him now. The party is his to lead. The parliamentary rebels must let him lead it. But he must also set out more clearly how it is he intends to take them out of opposition and, yes, back into government.