The NT is written as a historical document or letters, so is it heretical to assume that it is really addressed to our generation?

Everything in the NT is addressed to people living in the first century, about past, present or an imminent fulfillment. So why do people read it as if God wrote all that stuff to them? For example, is this a command and promise for the disciples or for the disciples and every generation since?: >[Mat 4:19 NIV] "Come, follow me," Jesus said, "and I will send you out to fish for people."