What does Sonnet 116 mean?
"Let me not to the marriage of true minds/ admit impediments"
The phrase "true minds" suggests an elevated rather than physical love. With a love of this kind, no obstacles should interfere. A marriage of true minds should withstand any storm, including the ravages of time. This type of love is unchanging, an "ever fixed mark". Unlike other loves that could be tossed about by tempests and destroyed, this love is solid, like the star that guides the lost at sea (every wandering bark). Because it is not a lust or a body driven love, the usual mortal complaints don't apply. Time may ravage the body, affecting such external qualities like the rosiness of lips and cheeks, but a marriage between true minds--that is true, exalted love--will continue despite the ravages of time. And this is what it means to love.
The principal theme of Sonnet 116 is that love is constant despite the corrosive power of Time and chance. The sentiment expressed here was familiar to Shakespeare's readers and to us from the customary marriage ceremony.
At the start of the sonnet's third quatrain, the narrator asserts even though Time inevitably exacts its toll on physical beauty and leads to the "doom" of mortality, true love remains. "Love's not Time's fool" captures the gist of the sonnet as a whole.
The ending couplet, though, injects a false note into the text. The narrator challenges others to the impossible task of disproving his argument that true love is constant and then uses both his own verse and the existence of love at-large as his proof.
It is trying to tell you that even though this person may be attractive, you may not love her as much. Love is a strong element of fate and desire and emotional love would never change. You may even love the person you regard as an enemy. He is trying to say that love would endure forever. Shakespeare is trying to compare love to a marriage- a life-long commitment that people have to make to consider really true love. If your love to each other is complete, it would have conquered time and bend changes as your love for each other would never die down and it would be everlasting. If your love for each other is strong, it would defeat time, day and even death itself.