Ahead of Thursday's crunch meeting of world leaders in London, Mr Brown will say it is vital banks relearn common values like honesty and responsibility.
US President Barack Obama will arrive in the UK later on Tuesday.
Scotland Yard is describing the G20 policing plan as one of the largest, and complicated public order operations it has ever devised.
Mr Brown's speech to faith and charity leaders at St Paul's Cathedral in London will emphasise that he understands the "pain" the recession is causing.
"In our families we raise our children to work hard and to do their best and do their bit," he will say.
"We don't reward them for taking risks that would put them or others in danger, and we don't encourage them to seek short-term gratification at the expense of long-term value.
"And in Britain's small businesses, managers and owners do not train their teams to invest recklessly, behave secretively or keep their biggest gambles off the books.
Ring of steel
Some 84,000 police man-hours have been allocated to the entirety of Operation Glencoe, the G20 security strategy. All police leave has been cancelled in London for Wednesday and Thursday.
Six police forces are part of the £7.5m security plan. The Metropolitan Police is leading - but also calling in colleagues from the City of London and British Transport Police.
Outside of the M25 motorway, officers from Bedfordshire, Essex and Sussex will have critical roles in securing the arrival and transfer of delegations to their virtual bunkers in embassies and hotels.
Inside the capital, police will co-ordinate the movement of these entourages and create a sterile environment at the Excel centre, base for the talks in East London's Canning Town.
Meanwhile on Monday, as the security provisions were being put in place, the prime minister said he believed world leaders will "rise to the challenge" of tackling the economic crisis and were "prepared to do whatever is necessary" to solve it.
One of a series of world leaders to visit 10 Downing Street in the lead-up to the summit was Mexican President Felipe Calderon.
Last week, the UK prime minister visited countries including the US, Brazil and Chile, promoting calls for a co-ordinated fiscal stimulus.
In an interview with the Financial Times, US President Barack Obama said: "With respect to the stimulus, there is going to be an accord that G20 countries will do what is necessary to promote trade and growth.
"The most important task for us all is to deliver a strong message of unity in the face of crisis."
