If on one side of the island of Christianity there is the dangerous water of Legalism as taught not only by Rome but many others, there is also on the other side of the island the danger of Antinominianism. Mark Jones at Meet the Puritans provides a more complete explanation, including a quotation from the real Francis Turretin to assist the reader in distinguishing between Justification and the entirety of the New Covenant (link). Legalism suggests that men are justified by works, whereas Antinomianism has no use at all for the law in the life of a Christian. Both errors ought to be avoided.