In the poem "A Contemplation Upon Flowers," the main contrast is the way flowers view death versus the way the poet views death.
The flowers have no fear of death. In fact, they are ever present in death. They decorate the bier at death looking "fresh and spruce."
The poet asks the flowers to teach him to view death differently. The poet fears death but in contrast the flowers have no fear of death.
The flowers are fragrant even in death. The poet desires to have sweet breath in death much like the flowers. The poet desires to breathe sweet fragrances as he dies.
The flowers seem to understand their purpose more so than the poet. The flowers bloom with no vanity. Then they die and go back to the earth from which they are born. There is no fighting death. The flowers obey and wither in dignity.
The poet sees the contrast in the way he accepts death versus the way the flowers so "gallantly" die and go back to the earth.
The poet contrasts his outlook on life to that of flowers. He does so by directly addressing the flowers, calling them brave. The flowers, he thinks, are in harmony with nature as he is not. As he puts it:
You do obey your months and times, but I
Would have it ever Spring
In other words, the poet wants to hang on to youth (Spring) and the good times it represents, while the flowers accept what comes.
The flowers, unlike the poet, are cheerful and modest despite their beauty and their "embroidered garments."
The poet grows more impassioned as the poem continues, as can be seen by the exclamation points at the end of the second stanza and in the third. In the third stanza, he asks the flowers to teach him how to accept death, rather than to fear it:
O teach me to see Death and not to fear,
But rather to take truce!
The unassuming peace and acceptance that he perceives in the flowers become the longed for contrast with himself.