I call it a policy because it something that was institutionalized by the Church much later and for reasons which have nothing to do with anything that can be found in the Bible. The policy was instituted at the First Lateran Council in 1123. At that time there were huge corruption issues in the Church, specifically nepotism and simony were big issues in the Middle Ages.
Now as for the full job description for service in the clergy, look no further than the New Testament:
” This is a true saying, if a man desire the office of a bishop, he desireth a good work. A bishop then must be blameless, the husband of one wife, vigilant, sober, of good behavior, given to hospitality, apt to teach; Not given to wine, no striker, not greedy of filthy lucre; but patient, not a brawler, not covetous. One that ruleth well his own house, having his children in subjection with all gravity; For if a man know not how to rule his own house, how shall he take care of the church of God? Not a novice, lest being lifted up with pride he fall into the condemnation of the devil. Moreover he must have a good report of them which are without; lest he fall into reproach and the snare of the devil.”
1 Timothy 3:1-7
There you go. The complete job description for service in the clergy directly from the Holy Bible. Why would anyone want to change it?
A secular mindset could not see the beauty of sacrifice and the Grace that flows from something freely given.
In the OT, priests had to abstain before they offered sacrifice to God. Since ours offer daily Mass, and Mass is a sacrifice, they would have to abstain completely if married. This is way the Orthodox do not have daily liturgies.
St Paul was writing to those already married who may have had children, the man chosen would then be perfectly continent and his family would be cared for by the local church. Obviously this would only work well in a small group situation.
I will leave it here as my spouse it demanding my attention and I have way too much to do today.