Look with mercy (Ps. 24:16-18) on these follies, Lord,
and deliver us (Ps. 78:9) who now call upon you.
Deliver also those who do not as yet pray,
that they may call upon you and you may set them free.

St. Augustine, Confessions, Book 1 (16)

St. Augustine became a Christian at about the age of 32.  So he is probably remembering his life before his conversion and he is praying for all the people who are now the way he once was, trapped in the slavery of sin.  In his auto biography, Confessions, he writes almost half the book about his life before his conversion and Baptism, and this prayer is one of many that shows his desire to ask God to help the unbelievers, to believe.  It is also a beautiful example of humility, combining both a prayer of contrition (1st verse) and intersession (2nd verse).