Final answer:
The line from Marvell's poem that encapsulates 'carpe diem' is 'Now let us sport us while we may,' urging to make the most of present moments before youth and beauty fade.
Step-by-step explanation:
The line from Andrew Marvell's "To His Coy Mistress" that best reflects the Roman poet Horace's idea of "carpe diem" or "seize the day" is "Now let us sport us while we may". This line captures the essence of living in the present and making the most of the time we have, which is at the heart of Horace's philosophy. Marvell's poem, much like the sentiment in Horace’s writings, urges the mistress to make the most of the youth and beauty they currently possess before it fades away. The urgency is further prompted by the imagery of fleeting time and the transience of life, as symbolized by 'Time's wingèd chariot hurrying near' in another part of the poem.