Longfellow was not Catholic. I don’t know how he felt about Catholicism but his translation of Dante, and these sonnets, amazing meditations on confession, are evidence of a sympathy at least. He was friends with Nathaniel Hawthorne whose daughter Rose became a Catholic nun. She is currently listed as a Servant of God. He also knew Orestes Brownson who converted in the 1840’s.
I enter, and I see thee in the gloom
Of the long aisles, O poet saturnine!
And strive to make my steps keep pace with thine.
The air is filled with some unknown perfume;
The congregation of the dead make room
For thee to pass; the votive tapers shine;
Like rooks that haunt Ravenna’s groves of pine,
The hovering echoes fly from tomb to tomb.
From the confessionals I hear arise
Rehearsals of forgotten tragedies,
And lamentations from the crypts below
And then a voice celestial that begins
With the pathetic words, “Although your sins
As scarlet be,” and ends with “as the snow.”
With snow-white veil, and garments as of flame,
She stands before thee, who so long ago
Filled thy young heart with passion and the woe
From which thy song in all its splendors came;
And while with stern rebuke she speaks thy name,
The ice about thy heart melts as the snow
On mountain heights, and in swift overflow
Comes gushing from thy lips in sobs of shame.
Thou makest full confession; and a gleam
As of the dawn on some dark forest cast,
Seems on thy lifted forehead to increase;
Lethe and Eunoe—the remembered dream
And the forgotten sorrow—bring at last
That perfect pardon which is perfect peace.