Lockwood hired the young man as an assistant in his law firm, while encouraging him to study at night and later to attend New York University, where he was a member of the Sigma Omega Psi fraternity.

Through the 1920s and the 1930s Goldstein's stature grew in importance as he rose from being a legal aide in state assembly committees to a political advisor in housing and other New York City affairs.

As he began his first term, Goldstein realized that twelve years of one-party control of the Attorney General's office resulted in abuse of the patronage system, with political appointees whose annual salaries exceeded $10,000 not showing up for work, while receiving their paychecks by mail.

However, another long-investigated and much-publicized case, which he personally supervised, had as its goal the withdrawal of the New York State charter for the Ku Klux Klan, which the organization had managed to clandestinely acquire in 1923.

He was quoted in a statement issued by the office of New York Attorney General, that "the principles of hate, intolerance, bigotry and violence must be stamped out" as he transmitted to the Federal Bureau of Investigation 1100 names of members of the Ku Klux Klan and the Hitler-resurgent German-American Bund.

He was a trustee of the Fletcher School of Law and Diplomacy and chairman of the board of overseers of the Harry S. Truman Research Institute for the Advancement of Peace at the Hebrew University of Jerusalem.