It is Not Befitting to Allah that He should Beget a Son

Muslims often quote this verse from the Quran:

It is not befitting to (the majesty of) Allah that He should beget a son. Glory be to Him! when He determines a matter, He only says to it, "Be", and it is.
--(Quran 19:35)


This is hard to answer until you realize that you should not disagree on this point.  Christianity differs from Islam in that it sees itself as a rescue mission to save man from sin.
The birth, life and painful death of Jesus shows how far God had to go to save us.  Jesus had to jump into the dirty world of humanity to pay the price for sin and bring us to God.  Is this dignified?  It is just what God had to do to save us.
 After you understand the price God paid to save us, you will willingly worship Him.

Also you should be aware that Muslims often believe that Jesus was the result of a physical union between Allah and Mary (this explains the second part of the verse above).