In the early part of his life, John Donne wrote poetry about love—he was, in fact, a partier and a womanizer. However, as he grew older—and perhaps because of his marriage and his growing faith—his poetry became more religious in nature. In his later years, he created work very much different than of his younger years.
For the enormously complex and vexed John Donne… life was love—the love of women in his early life, then the love of his wife (Ann More), and finally the love of God.
In Donne's Holy Sonnet 6, the theme is very religious, addressing specifically his death, his separation—body from soul, his fear of God, and his hope that when he died, his sins would remain earthbound, as would his flesh and "the devil."
He refers to his life as a play; and he is approaching the "final scene." He is finishing his pilgrimage, and the end of his life approaches. He personifies death, describing how eagerly (hungrily) it will break apart his body and soul:
And gluttonous Death will instantly unjoint
My body and soul...
Donne believes he will then sleep for a while; but when he wakes, he will come face to face with God, who puts fear into every part of him—so that his body shakes:
But my ever-waking part shall see that face,
Whose fear already shakes my every joint.
As his soul flies up to heaven, his physical, "earth-born" body will remain below, and the author hopes that his sins will also remain—though without salvation, they would "press me to hell." He hopes that God will grant him righteousness and "purge" him of evil—and he will leave all behind...
...the world, the flesh, the devil.
Donne's Holy Sonnet 13 also has a religious theme, but it concentrates now as a warning of sorts. He asks the sobering question, What if the world was going to end tonight?
What if this present were the world's last night?
He then addresses his heart, telling it to take note of its place in God's will: he considers the "picture of Christ crucified," and wonders if his Lord's face can frighten him. Christ's tears block out the light of glory. Blood from the crown of thorns fills the frown lines on Christ's face.
Tears in His eyes quench the amazing light;
Blood fills his frowns, which from His pierced head fell...
The poet wonders then if his Savior's tongue could send his soul to hell...when it was the same tongue that called for forgiveness for those who crucified him—alluding to "Father, forgive them, for they know not what they do" (Luke 23:34, ESV):
And can that tongue adjudge thee unto hell,
Which pray'd forgiveness for His foes' fierce spite?
But then the poet recalls—when he worshipped ("idolatry") worldly things. In the days before he became a devout believer, he would tell his mistresses that there was nothing wrong with beauty, even though it was called "foulness"—for it was simply someone's judgment or a label—words without substance. But the poet then addresses his soul again, with a change of heart—for he is no longer the man speaking to a mistress, in an existence that lived only for pleasure. He now sees those words through converted eyes: his faith is such that he sees his old life as one filled with mistakes that he cannot countenance (tolerate) now: he declares that wicked spirits may be made to look horrid, but that beauty can also hide a piteous ("pathetic") mind.
Donne's early worship of beauty never understood that wickedness might lie within, but he understands much more now.