Why does Foner say that the New Deal “transformed the role of the federal government”?

Prior to the Great Depression, the prevailing consensus was that the Federal government had a very limited role to play in running the economy. According to the doctrine of laissez-faire, the Federal government should simply establish the legal and regulatory structure in which businesses operate and allow the free market to determine the production and allocation of goods.
In the aftermath of the Wall Street crash and the ensuing Depression, this reigning economic orthodoxy was challenged. Many now believed that lack of effective government regulation of the economy was partly to blame for the economic catastrophe that had descended upon the country. But according to such critics, tighter regulation wasn't enough; the government had to get directly involved in running the economy.
It was this attitude that finally prevailed with the election of Roosevelt in 1932. Under his New Deal, the role of the Federal government, not just in relation to the economy, expanded rapidly in a manner that until recently would have been unthinkable. The new consensus held that it was perfectly legitimate for the government to create jobs through massive public works projects such as the Works Progress Administration, or WPA.
The New Deal also established a Federal system of Social Security, which still exists to this day. For the first time, the principle was established that the Federal government should establish some kind of safety net for seniors, who previously had to rely on their own savings, help from their families, or private philanthropy.
Americans have always had an inherent suspicion of over-mighty government, seeing it as a threat to their hard-won liberties. The Revolution against the British was fought on just such grounds. Yet thanks to the New Deal, a growing number of people in the United States began to accept that government control in some areas was not just a necessary evil, but actually a positive good, conducive to giving people freedom from the indignities of poverty, unemployment, and want. The New Deal had vastly expanded both the size and scope of the Federal government, and though future administrations would attempt to cut back on what they saw as "big government," there was to be no going back to the days of laissez-faire.