I’m standing to be leader of the Labour party for the simple reason that if I don’t, certain necessary truths may go unspoken during the debates of the coming months.

A leadership competition is not an ideal context for honest reflection. The aim is, after all, to win, not to learn and build. In a divided party, there is always a danger that factions will overcome facts; or, with a compromise candidate, that triangulation will trump truth. I want to break this cycle: to use the leadership campaign as an opportunity for us all to learn from each other, and to help our party grow.

That’s the first reason I’m standing: for a chance to tell the truth. With our party on the edge of a precipice, now is the time to dispel our fears and face up to reality. Anything else would mean that the millions of people who still need a Labour government, so badly, would be failed again.

The truth is that to change our country, we have to change ourselves.

Last week’s crushing defeat now poses two simple questions. Why did we lose? And how do we win?

The truth is that despite his enormous achievements in inspiring a new generation of members, Jeremy Corbyn’s first promise as leader was never fulfilled. The party was never democratised on the scale or to the extent that members were led to expect – they were never empowered to campaign, select candidates or determine policy on the scale that was required. This must now change. We don’t need foot soldiers, we need an army of activists who think critically, treat each other with respect and have a serious democratic stake in the movement. I don’t want to manage the labour movement, I want to unleash it. That is the first route to victory.

The truth is that while making a clear break with the New Labour era in terms of policy and personnel, the party was never able to communicate this to voters in our heartlands. When trying to persuade them of our radicalism and sincerity, we often had the legacy of the 2000s thrown back in our faces. Persuading voters that we understand the sources of their long-held resentment and frustration, of their disappointment in how Labour has conducted itself since the 1990s, will be the first step towards winning back their trust.

The truth is that indecisiveness and triangulation on the Brexit issue saw Jeremy’s favourability ratings fall from positive to catastrophic after the June 2017 election. Such prevarication and lack of leadership must never characterise our politics again.

The truth is that after Jeremy became leader, we fought two elections on an electoral system that massively favours the Conservatives, and their voter base of propertied pensioners. A majority of the British public voted for parties of the left or the liberal centre. But this was in no way reflected in the election result. Labour should have committed itself to changing the voting system decades ago, and we have condemned some parts of our country to 40 years of decline by failing to do so.

But to go forward from this point we must tell the truth, not just about what went wrong, but also about what kind of society we believe in. In 2019, we offered some of the right abstractions about promoting equality and opposing austerity. But we never painted a rich and textured picture of life in the society that we proposed to build. Instead we offered a shopping list of rather disconnected policies.

It’s not such lists people live their lives by, but emotions and feelings. My vision for the country is of warmth and energy. A country that starts every conversation and every project – either in business or politics – with a belief in the best in people. This is the hopeful creed of a 21st-century socialism. It is what motivates our members and our most passionate supporters.

Any politics animated by such a positive vision must also be prepared to stand and fight against its enemies, those who degrade our society for their own benefit. Many of our towns have never recovered from the catastrophe of Thatcherism. Young people can’t find homes or meaningful work. Old people struggle without the care they need. None of this has happened by accident, or because of some technical error. It is the result of systematic efforts by the elite, which Boris Johnson represents, to plunder our country to their own advantage.

They will seek to divide us by blaming immigrants and other vulnerable people, and we must not let them.

Two forces will shape our future, and the context of the next general election: the climate crisis and the ongoing technological revolution. Both can be sources either of despair or hope. We can hide behind platitudes and denial, or we can seize these crises as opportunities to renew our country as it has not been renewed since the 1940s.

Everything is down to us and how we react to these changes. Do we seek rich lives within nature’s boundaries, or the desolation that Johnson’s brand of disaster capitalism will ensure? Do we seek a connected, collaborative and more equal society or a world of perpetual surveillance and exploitation?

To convincingly offer such a vision and respond to the hope and fears of climate and technology we need a different kind of party. One that is open, democratic, inquisitive and that expresses solidarity with others inside the party and outside. Labour must be the anchor of a broad movement for change.

We can start to transform the party now. I don’t want to beat the other candidates; I want to learn from them and with them. I want us to use this campaign to reach out to every other progressive force in the country – parties, campaigns and movements – for the biggest conversation possible about how, together, we can change our country for the better. Nothing else will do.

Even at this dark hour, as Labour suffers its own Dunkirk, as retreat is forced on us, I’m an optimist. And my hope is founded in the unshakable belief I have in all of us. People are amazing. Given the support, care and time we can do incredible things. Our job, in the words of Raymond Williams, is “to make hope possible, not despair convincing”. Labour can and must offer hope: not the falsehood that it will do everything, but the real promise that it can help us help each other.

• Clive Lewis is Labour MP for Norwich South and shadow minister for sustainable economics