What is the rationale for forbidding priests to marry in traditions where already-married men are allowed to become priests? As everyone knows, married men are unable to be ordained as priests in the Latin Rite of the Roman Catholic Church, nor are priests allowed to get married for as long as they remain priests. This is not quite the case in other ancient churches. According to Wikipedia, married men are allowed to be ordained as priests in the Eastern Orthodox, Oriental Orthodox, and Eastern Catholic traditions, but even in these traditions unmarried priests are not allowed to get married after ordination.

What is the rationale for allowing men to marry and then become priests, but forbidding them to become priests and then marry?
I am a part of the Antiochian Orthodox Church.

I asked my Priest this (who is married), and what I recall him telling me is it has to do with the fact that if you were allowed to marry after becoming a priest, things regarding courtship and all that are likely to get in the way of being an effective and focused priest. Whereas if you are already married, then all that drama is out of the way, and though that does give you a family to concern yourself with in addition to the Church, you are firmly grounded and it doesn't get in the way of being the kind of priest you should be.

But you are allowed to become married and then become a Priest because Marriage is considered a Sacrament, and so to experience this Sacrament as laity, as long as you are being the husband / father you should be, then it is still acceptable to become a Priest (and in having a wife it's easier to not give in to earthly desires).  Personally I think this is a much more grounded and sensible reasoning than saying you cannot become a Priest if you are married.

This is what my Priest sent me:


  1) "the husband of one wife" (I Timothy 3:2) this is from the Pastoral
  Epistles of St. Paul.  This has been the core teaching on the
  priesthood since it was written. 
  
  2) the generally, the priests are held to the standard that all
  Christians called to, but often don't live up to.
  
  This may give you a little background if you'd like it: 
  http://www.firstthings.com/web-exclusives/2015/10/of-marriage-and-orthodox-priests


It is the view that celibacy is better, as is described in that article and by my Priest.  And one such Bible reference example comes from 1 Cor 7:


  [32] But I would have you without carefulness. He that is unmarried
  careth for the things that belong to the Lord, how he may please the
  Lord: [33] But he that is married careth for the things that are of
  the world, how he may please his wife.


But thankfully it's also recognized that celibacy is a very high calling, and fares better for monks rather than priests.