In the first stanza of the poem, ‘angels’ are some heavenly figures, generally beyond our reach. Symbolic enough, it refers to the unattainable height she wishes to reach.

And, in the fifth stanza of ‘I Believe’, the poet-speaker feels she is ‘amidst the human angels’. She is confident that she ‘can do many things’, for she is surrounded by those angels. Here, ‘angels’ are successful and great persons who inspire us and who have got the status of ‘angels’ for their greatness.

So, in short, the first ‘angels’ signifies attaining the unattainable, and the second one refers to the great personalities.

In the first stanza the angels are the spiritual aspirations of one human being who desire to be something in their life. They are some sort of the heavenly creatures that guide people to follow the path of righteousness whereas in the last stanza the human angels are the good and better human beings who have achieved something in life and left a mark in the global arena by their good deeds.