The first two lines of this twelve-line poem,...
Ben Jonson (a contemporary of William Shakespeare) writes "On My First Son," speaking of the death of his seven year-old son.
Farewell, thou child of my right hand, and joy;
My sin was too much hope of thee, lov'd boy.
The first two lines of this twelve-line poem, express Jonson's farewell to the son he loved so much. The reference to "my right hand" might be a Biblical allusion to Christ, God's beloved son who sits on God's right-hand side. The boy was his father's "joy." Jonson admits that his sin was to expect that the boy would have a long life because:
Seven years thou wert lent to me, and I thee pay.
Exacted by the fate, on the just day.
...Jonson says he believes that for seven years, the boy was his only on loan—we assume, from heaven—and payment was taken in the form of the boy's life on the day he died (of the plague, while Jonson was away).
Oh, could I lose all father now! For why
Will man lament the state he should envy?
The first sentence in the second quatrain (four-line stanza) could mean that Jonson no longer wants to feel the pain of being a parent and losing a child, or, wishes he could be like a child to express his grief without reservations: freely and "wildly" as a child would. The rest of this segment is the author's way of wondering why he should be sad ("lament") the state his son is now in—in heaven, without pain—which is something one should envy (as per the teachings of Christianity).
To have so soon 'scaped world's and flesh's rage,
And, if no other misery, yet age?
The second part of the second quatrain explains that the boy has escaped the ravages of time: old age. And is this not a blessing for the boy? The author is trying to now comfort himself in his grief, while he may also be doubting his faith a little: he has been taught that this rest—this peace—is to be sought after according to the Christian faith.
Rest in soft peace, and asked, say here doth lie
Ben Jonson his best piece of poetry;
In these first two lines of the third quatrain, Jonson addresses his son, wishing him "soft peace" as he rests; he also hopes that all who pass the grave can know that there lies what is left of Jonson— his "best piece of poetry:" his greatest work beyond all he has ever written or done.
For whose sake, henceforth, all his vows be such,
As what he loves may never like too much.
In this last part of the third quatrain, Jonson hopes that of all the promises he makes to himself, he hopes he can fulfill the one that swears he will never again allow himself to love another as much as he loved his son, so as to avoid feeling this kind of pain again.