The line from Lincoln’s speech that best corresponds to King’s concern when he writes, “We have waited for more than three hundred and forty years for our God-given and constitutional rights,” is:
“It is for us the living, rather, to be dedicated here to the unfinished work which they who fought here have thus far so nobly advanced.”
This line emphasizes the idea of continuing the struggle for equality and justice, reflecting King's call for action and the need to address the long delay in realizing rights for all.