Why do Nora and Torvald feel optimistic about their future at the beginning of Act 1 ?

It is Christmas Eve in the Helmer family's apartment, which is furnished “comfortably but not extravagantly.” Nora enters with parcels, leaving a porter at the door with a Christmas tree, which she tells a maid to hide so that her children will not see it. She nibbles on some macaroons she has bought, but she hides them too when her husband, Torvald, comes out of his study. Torvald has recently been given a new job as a bank manager. Discussing her purchases with him, Nora is keen to spend more money, believing that her husband’s new job will mean that the family no longer has to be careful with money.