In Richard Lovelace's poem, "To Althea, from Prison," the poet "does" several things. Paradoxically, this poem discusses the contradictions between the sense of captivity and freedom.
The author can freely express his opinion while in prison: no one has gagged him. The author can still enjoy his feelings of love. No prison can rob him of this.
He also can find peace in his guiltlessness. This is expressed in the following lines:
Stone walls do not a prison make,
Nor iron bars a cage;
Minds innocent and quiet take
That for an hermitage;
This means that being imprisoned and being a prisoner are different things. Just because he is in a prison does not mean he is not free: his mind is innocent and so he can simply spend quiet time in reflection, as one might on a hermitage (or a religious retreat). The reference to a "hermitage" might also suggest that he is free to "converse" with God during this quiet time allotted to him.
And at last, though bodily confined, the author stresses that he may still enjoy the freedom of his soul, which cannot be confined, and he compares his freedom to that of the angels.