What does Daniel 11:17 mean?

Daniel received these prophecies in 536 BC (Daniel 10:1; 11:2). The events predicted include the rise and fall of Alexander the Great (Daniel 11:3–4) and the wars fought between the kings of Syria—leaders of the Seleucid Empire—and the Ptolemy dynasty of Egypt (Daniel 11:5–12). Ultimately, Antiochus III, known as "Antiochus the Great," assumed firm control over the lands of Judea (Daniel 11:13–16). By then, the early second century BC, the Roman Empire was a growing threat. Rather than fight on two fronts, Antiochus attempted to control Egypt through diplomacy.

To "set his face" means to come to a firm decision. As this verse predicted, Antiochus arranged the marriage of his daughter to the Egyptian king. Her name, Cleopatra, would persist in the dynasty; around 150 years later it would be given to the famous Egyptian queen associated with Marc Antony of Rome. Antiochus's goal was probably to weaken Egyptian hostility and turn the nation in his favor, to aid some later conquest. His tactic worked, at first. Cleopatra I Syra took on great power and staved off efforts to reignite a war with the Seleucids.

This verse notes that Antiochus's attempt would not ultimately succeed. On her death, Cleopatra I passed authority to two advisors, who soon declared war.