What is the main difference between “jāʾa rajulun” and “jāʾa al-rajulu”?

Supplementary Practice 9: How Small Wording Changes Alter Rhetorical Meaning

• The first may introduce a man; the second points to an identifiable man
• The first denies the man’s learning; the second establishes it
• The first is past; the second is imperative
• The article must express magnification in the second