Translation:

21. He said: "So (it will be): thy Lord saith `That is easy for Me: and (We wish) to appoint him as a Sign unto men and a Mercy from Us': it is a matter (so) decreed."

Notes (Tafseer)

2473. The mission of Jesus is announced in two ways (1) he was to be a Sign to men; his wonderful birth and wonderful life were to turn an ungodly world back to Allah; and (2) his mission was similar to that of all prophets of Allah. But the point here is that the Israelites, to whom Jesus was sent, were a hardened race, for whom the message of Jesus was truly a gospel of Mercy.

2474. For anything that Allah wishes to create, He says "Be", and it is (Cf. iii. 47). There is no interval between His decree and its accomplishment, except such as He imposes by His decree. Time may be only a projection of our own minds in this world of relativity.