His sadness has made him witty, as he rationalises it.
His sadness has made him depressed, as he dwells upon it.
His sadness has reduced him to a fool, as he does not know the cause of it.
He is worried about the safety of the ships in whose cargoes he has invested his wealth.
He is worried that the investment he made in business will not yield returns.
He is worried that his cargo may not reach its destination on time.
The two men may be brothers.
The two men are similar in character.
The two men are foils to each other.
Bassanio is a learned man whom Antonio respects.
Bassanio is older than Antonio, and the latter seeks his advice.
Bassanio is a close friend and companion of Antonio.
He is blunt and rude, and offends others deliberately
He is talkative and witty, and scorns pretentiousness
He is honest and wise, and gives sound advice
Gratiano is implying that Antonio may be putting on an act, that he is pretending to me melancholic in order to appear thoughtful and wise.
Gratiano is implying that Antonio is introverted by nature, and thus appears sad to others.
Gratiano is implying that Antonio is proud, as he makes known his sadness, and wants others to give in to him.
The mission to win the lady's hand is to be kept secret.
The mission to win the lady's hand is a quest, a journey.
The mission to win the lady's hand requires the involvement of many people.
"... but my chief care/ Is to come fairly off from the great debts/ Wherein my time, something too prodigal,/ Hath left me gagged."
"... How much I have disabled mine estate/ By something showing a more swelling port/ Than my faint means would grant continuance."
"To you, Antonio, I owe the most in money and in love..."
He promises to lend Bassanio money from the profits of his cargo
He promises to accompany Bassanio on the journey to win Portia's hand
He promises to obtain money for Bassanio on credit