The unifying theme of Sonnet 31 and 39 is?

Sonnet 31 and Sonnet 39 contain the unifying theme of love and its power. In Sonnet 31, the speaker compares his love to a summer day, describing it as "more lovely and more temperate." He then goes on to say that his love will never fade, even as the summer day eventually gives way to winter. Similarly, in Sonnet 39, the speaker compares his love to a "precious jewel" that is "more dear than gold" and "more rare than Eastern pearls." He then goes on to say that his love is so strong that it can withstand any obstacle, including the passage of time. Both sonnets express the speaker's deep and abiding love for his beloved, and both use imagery and metaphors to convey the strength and beauty of that love.