https://www.theguardian.com/commentisfree/2014/mar/17/george-herbert-poetry-faith-vocation
The poem takes its title from the parable of a perfect pearl hidden in a field: a man finds it, and goes and sells everything he has so that he can buy the field and own the pearl. In the final verse, Herbert uses this metaphor of buying and selling to great effect, making it clear that he went into the bargain of ordination with his eyes open:
“I fly to thee, and fully understand / Both the main sale, and the commodities.”
How my heart sings 