It will feel personal for the prime minister whose judgement has been attacked in recent days following the loss of his US ambassador, Peter Mandelson, and his deputy, Angela Rayner, leading to a major ministerial reshuffle.
Sir Keir has also seen the departure of a number of key aides from Downing Street as he seeks to bolster his communications strategy, which appears to be failing to cut through with swathes of the British public if dire opinion polls for the party are any indication.
It is not just opinion polls – the prime minister will also need to steer his government through a very difficult budget in November, with Chancellor Rachel Reeves signalling she is likely to need to raise taxes to deal with the worsening economic forecast.
A brief preview of the speech released to reporters in advance indicates that Sir Keir will seek to appeal to those beyond Labour, including those who have never voted for the party, and ask people to question whose side are they on – his or Reform’s.
“It is a test. A fight for the soul of our country, every bit as big as rebuilding Britain after the war, and we must all rise to this challenge,” he will say, warning that the goal will not be achieved without a cost.
“We need to be clear that our path, the path of renewal, it’s long, it’s difficult, it requires decisions that are not cost-free or easy,” he is expected to say.
“Decisions – that will not always be comfortable for our party. Yet at the end of this hard road there will be a new country, a fairer country, a land of dignity and respect.”
He will also talk about rebuilding, in a nod to Labour Prime Minister Clement Attlee’s postwar government’s programme of new towns, which fixed the devastation wreaked by bombs as well as poverty.
The party promised at the weekend to start building three new towns in England before the end of the decade.
The prime minister will urge the country to “unite around a common good” aiming to improve living standards, grow the economy “from the grassroots” and put “money in the pockets of working people”.
“We can all see our country faces a choice, a defining choice,” he will say.
“Britain stands at a fork in the road. We can choose decency, or we can choose division. Renewal or decline.
“A country – proud of its values, in control of its future or one that succumbs, against the grain of our history, to the politics of grievance.”
Sir Keir is trying to build a foundation for his party to continue to back him through what could be deep and painful losses to Reform UK in May’s Welsh, Scottish and English local elections.
He knows that plenty in his party, from the cabinet down, are privately pondering whether this could be his last Labour Party conference as prime minister.