Just because God separates a man in his mother's womb to this great task of preaching does not mean that he will not face a great many struggles in the process of becoming a preacher.
We may well call certain men "Born-Preachers" because from the word go they seem to have this unique gift of preaching and immediately ascend to the clouds when they open their mouths. But this is not the normal and is not the picture painted in Scripture of a God-born preacher. In the Old Testament we read of true God-called men and preachers birthed amidst impossible situations, surrounded with great difficulties and filled with inward infirmities and doubts.
Few older preachers explain and make clear to younger preachers, the difficulties, failures and struggles in coming forth as Gods mouth-piece.
When Jeremiah was called of God and it was revealed unto him that the Lord (unknown to man) had separated him to such in the very womb all he could say is "Ah, Lord GOD! behold, I cannot speak: for I am a child.” At that very stage the Lord revealed to him that his message would be such that everyone would be against him but from God's view-point he would be against everyone. The Lord warned him that if he didn't speak all that He gave him to speak then the Lord would confound him. Even later in ministry when this was fulfilled and men rejected him and scorned his message he said, "I will not make mention of him, nor speak any more in his name. But his word was in mine heart as a burning fire shut up in my bones, and I was weary with forbearing, and I could not stay." (Jer 20:9)
These are the trials that will most certainly face a young preacher especially in an hour of apostasy in the church as our day is. Discouragement may come, even terrible despair, but the Word of God will burn in the heart and bones of a true prophet or preacher.
Just recount the history of God-called men and you will see the many difficulties that birthed them forth into ministry. Moses had failed God terribly 40 years before and now seemed to lack any ability whatsoever to step forth into the calling. All he could say is "I am not eloquent" but that was the hour of his preparedness for God's purpose. Oh what inward and outward trials he must persevere through to be God's leader.
Then there was fearful Gideon who needed much assurance; David the young shepherd boy despised by his brothers and called proud; Samuel in the midst of utter apostasy, apathy and lukewarmness; Saul the greatest and most learned religious zealot who through conversion must become Paul the Apostle who counted all such religious zeal as dung; young timorous Timothy who felt his lack to minister in the churches but who must play the man and play his part.
All these and many many more must fight through the lack in their own personality and temparament, not to mention the surrounding impossible mountains of circumstances. But more than this. They must persevere in their calling as leaders and preachers when even God's people reject and despise them. That's hard. Enemies arise to oppose them, false prophets lie against them, political powers persecute them.
God-birthed preachers do not just pop out of the womb. They must travail with tears over their own personal inabilities and rely in faith upon God's ability. They cannot make up their own messages or steal other's, they must speak what God gives them. It is through all the inward struggles and outward opposition that God birth's forth a true preacher. Isa.48:10 "Behold, I have refined thee, but not with silver; I have chosen thee in the furnace of affliction."
One last thought. Gal.1:15-16, "But when it pleased God, who separated me from my mother's womb, and called me by his grace, To reveal his Son in me, that I might preach him among the heathen:" The first and greatest persecutor of the early Church who lived by the very breath of threats against Christ and Christians was in fact separated in his mothers womb to this great task of preaching. God does chose some of the most unlikely and most impossible for this great task of preaching.
While he was yet raging against the Christ of God; while he was fuming against the
message of His resurrection; while he was yet dragging parents from children and throwing them into prison; while he was forcing Christian men and women to blaspheme the name of Christ - all the while he was in realtity a born preacher. In his very birth, though it seemed impossible by his life, he had been separated by God's own hand and divine purpose to be a preacher, a born preacher!