Good question. There isn't one, and as you know some married men are allowed to become priests.
Celibacy of priests is a Latin tradition dating from the Middle Ages. It was firmly established by Pope Leo the Great. The underlying theology is that a priest is a vicar of Christ and is spiritually married to the Church, because Christ is married to the Church. If he is at the same time married in the usual sense to a woman, that creates a complication in his life because his loyalty is now divided between the Church and the earthly family. It can be allowed as a charity to a man already married who at the same time is called to priesthood. Fundamentally, a married priest is an exception, which became the rule for parish priests in Orthodoxy and Eastern Rites. Bishops are celibate throughout the Church.
None of that is in the Bible, at least not directly, so don't ask for verses. The Church does not operate in wonkish ways.
Please show me the verse about Christian men becoming priests.
Perhaps you didn't notice people accusing me of knowing nothing about the bible. Please go find those posts a couple back and splain to them that it isn't in the bible.