Firstly, one needs to understand that Antonio makes this loan not for himself, but for Bassanio, probably his closest friend. Bassanio, who seems to have gotten into the habit of using Antonio's kindness, had once again relied on his magnanimity to lend him money so that he may woo the beautiful and prosperous Portia from Belmont.
The nature of Antonio's situation can best be described as follows:
Since Antonio had invested practically all of his available cash in a few maritime ventures, and his trade-ships had not yet delivered their cargo, he had no immediate cash flow which he could use. He then advised Bassanio to obtain a loan in Venice by using his good name as guarantee. He would do likewise.
When Bassanio meets with Shylock, the Jewish moneylender, to make the loan with Antonio as guarantor, Shylock says the following about Bassanio's benefactor:
... my meaning in saying he is a
good man is to have you understand me that he is
sufficient. Yet his means are in supposition: he
hath an argosy bound to Tripolis, another to the
Indies; I understand moreover, upon the Rialto, he
hath a third at Mexico, a fourth for England, and
other ventures he hath, squandered abroad. But ships
are but boards, sailors but men: there be land-rats
and water-rats, water-thieves and land-thieves, I
mean pirates, and then there is the peril of waters,
winds and rocks. The man is, notwithstanding,
By saying this, Shylock further emphasises Antonio's insecure position.He finds Antonio a suitable and acceptable borrower. He mentions, however, that all Antonio's merchant ships are at sea, sailing to a variety of locations as well as other ventures he may have abroad, which to him, is a waste. Shylock mentions the risks inherent in Antonio's ships, such as encountering pirates, both on land and at sea, the perils of the winds and the danger of rocks which may destroy or damage Antonio's ships. He does, though assess Antonio apt enough for him to grant a loan to.
in addition to the above, the following also provides clarity on Antonio's position:
On his meeting with Antonio, Shylock expresses his resentment for the manner in which Antonio, a Christian, has been treating him. He has behaved in a most despicable and prejudicial manner. Antonio spat on him, kicked him like a dog, openly criticised his usury and tarnished his good name. Irrespective of Antonio's ill-treatment of him, Shylock agrees to the loan. He tells Antonio that he will not charge him any interest, but would demand a pound of Antonio's flesh if he should not repay the loan within three months.
The terms of the loan state that Shylock will lend Antonio three thousand ducats to be repaid within three months. If Antonio forfeits, he should sacrifice a pound of his flesh to him. Antonio agrees to these terms and Shylock asks him to immediately proceed to the notary to draw up the bond whilst he goes to fetch the money. Bassanio asks Antonio not to agree to the bond, but Antonio ironically expresses faith in the success of his ventures and says that Shylock has done him such a kindness and that he has gone soft to such an extent that he might become a Christian.
How right and how wrong Antonio's words would turn out to be!