Zuma said this as he was inaugurated in the nation's capital, Pretoria.
The national development plan, a blueprint for growth drawn up in his first term would be the major engine of 'radical' socio-economic change, said Zuma.
"It's time for us to do what we have always said we would, do not be alarmed when we take decisions that are hard and unusual, we will be doing it for your good," he told thousands of supporters gathered in Pretoria, speaking in his native Zulu.
The inauguration was attended by world leaders at the Union Buildings where Zuma, 72, was sworn in by the chief justice of the Constitutional Court.
Military airplanes flew above the Union Buildings forming the number 20, symbolising the years since South Africa's first democratic elections when Nelson Mandela ended centuries of white domination by becoming its first black president.
The South African economy has grown at a sluggish pace with high unemployment and inflation during Zuma's time in office and was last month overtaken by Nigeria as Africa's largest economy after it rebased its GDP.
Zuma's ruling African National Congress (ANC) won a slightly reduced majority in national elections earlier this month in the country's fifth post-apartheid elections.
A former anti-apartheid veteran and populist, Zuma rose through the ranks in Mandela's former liberation movement.
Zuma's first term was beset with scandals including one in which he was ordered by the Public Protector, the chief anti-corruption watchdog, to pay back some of the funds used to renovate his homestead.
As well as the longer term task of reviving the economy and tackling unemployment, Zuma faces the more immediate threat of unrest in many black townships and a strike in the platinum sector now in its fifth month - the longest in South African history.