Final answer:
The phrase "I swear to thee, youth, by the white hand of Rosalind" is a solemn promise made by a character in a piece of literature, using the hand of a character named Rosalind as a symbol of sincerity.
Step-by-step explanation:
The phrase "I swear to thee, youth, by the white hand of Rosalind" is from a piece of literature where a character is making a solemn promise or oath to someone using the hand of a character named Rosalind as a symbol of their sincerity. In this context, the phrase implies that the person speaking is giving their word and making a vow based on their trust in the mentioned character, Rosalind.
For example, in Shakespeare's play As You Like It, a character named Orlando pledges his love and faithfulness to a young man named Oliver using the phrase "I swear to thee, youth, by the white hand of Rosalind." Here, Orlando is emphasizing the sincerity of his promise by invoking the name and hand of Rosalind.