The later part of Raleigh's life was spent living imprisoned in the Tower of London under suspicion of plans to work with the Spanish to over throw the English king. Many of his most moving works, including The History of the World were published during this time period. It is believed that, fearing his own mortality, he wrote "To His Son" and a guide for his son who would be left to grow up without his father.
First notice that the poem is written in the style of Shakespeare's sonnets. Its 14 lines follow the ABAB, CDCD, EFEF, GG pattern mastered by Shakespeare. Also notice Raleigh's attention to "3". In the first stanza he addresses "Three things there be that prosper up apace" (1) and later he references “the Wood, the Weed, the Wag” in the second stanza, and again “Green springs the tree, hemp grows, the wag is wild” in the last stanza.
The first stanza begins with ambiguous descriptions. His three things are three different things that will meet up later in the poem. The Wood and the Weed symbolize the gallows and hangman’s bag; the Wag is his son (or a young boy). In the third stanza the wag begins to grow but needs someone to look after him and help him grow into a man.
Eventually all elements die (as Raleigh is also about to die). He ends his poem with
But when they meet, it makes the timber rot,
It frets the halter, and it chokes the child.
It is Raleigh’s hope that his son will grow strong, and not be affected by those who have judged and executed his father. Raleigh knows that his name has been ruined, and he hopes that his son, called Wat short for Walter, will not let these people ruin him too.