why we need passphrase

[Afzal, Naeem M]

Hi,

In order to understand GnuPG, I tried to create private keys on two ubuntu systems. Here are my steps and I would ask my question at the end as I need to show what I did.

1. System A: Created private and public key by using 'gpg --gen-key' and then
        'gpg --export --armor -out userA.asc -r 'USER A'

2. System B: Created private and public key by using 'gpg --gen-key' and then imported public key of userA
        'gpg --import userA.asc'

3. System B: encrypted a file for userA using userA's public key '
        gpg -o file_from_userB -r userA --encrypt file_to_encrypt

4. System A: Tried to decrypt file_from_userB
        gpg -o decrypted_file --decrypt file_from_userB
at this point, it asks to provide passphrase of userA. Is it possible to avoid where I need to provide passphrase at all? My understanding was that the file was encrypted with userA's credential to begin with, and userA should be decrtypt it without providing any passphrase? How can do this procedure where I don't have to provide passphrase in decryption?

Thanks a lot.

Naeem