Final answer:
Patrick Henry's speech uses the phrase 'holy cause of liberty' primarily to motivate, unify, and address doubts about the American Revolution, but it does not suggest that victory is predestined by God.
Step-by-step explanation:
In the excerpt from Patrick Henry's "St. John's Church" speech, the reference to "holy cause of liberty" serves to establish a sense of duty, suppress doubts about going to war, and inspire loyalty in the new government. However, the phrase does not primarily serve to "Support the belief that the colonists are destined by God to win." This option suggests a predetermined outcome, while Henry's speech focuses on the moral imperatives and efforts required to achieve victory, rather than predestination. Patrick Henry was known for his fervent support of the American Revolution and his famous declaration "Give me Liberty, or give me Death!" which emphasized his commitment to the pursuit of liberty, even at great personal risk.