In The Merchant of Venice, Antonio is a merchant who would never consider lending money to anyone and charging interest. He disapproves of the practices of money lenders and most specifically, Shylock. However, Antonio wants to help Bassanio secure a chance of having a future with Portia and cannot refuse him when he comes to Antonio after having squandered his own wealth - "disabled mine estate."(I.i.123) Antonio's own assets are tied up as his ships are "abroad." So Antonio has allowed Bassanio to seek out a loan - "try what my credit can in Venice do"(I.i.180) and hence, he now agrees to borrow from Shylock.
Antonio is very confident of his position as he will be able to realise his wealth very soon when his ships come in; in fact, his ships are expected at least a month before the "bond" will become due so he is more than happy to agree to Shylock's terms. Not only that but, Antonio is expecting a lot more than the value of the bond when his ships do arrive.