en_tn/1co/01/18.md

the message about the cross

''the preaching about the crucifixion" or "the message about Christ dying on the cross" (UDB)

is foolishness

“is senseless" or "is silly."

to those who are dying

to those who are dying - "dying" refers to the process of spiritual death.

it is the power of God

"it is God working powerfully in us"

frustrate the understanding of the intelligent

frustrate the understanding of the intelligent - AT: "confuse intelligent people" or "make the plans intelligent people make completely fail"