His career as a preacher began in 1544 where he first preached in Ross, and then in Dundee, where, with great admiration of all that heard him he expounded Paul's epistle to the Romans. At the instigation of the Cardinal, a certain man named Robert Mill tried to stop his preaching. He said to Wishart, in a public place, that he should not trouble their town any longer, that he would not suffer it to continue. Wishart thought about this for a little with his eyes raised up to heaven, and then looking sorrowfully upon the speaker and people, he said – God is my witness that I never intended your trouble, but your comfort; your trouble is more dolorous to me than it is to yourselves; but I am assured that, to refuse God's word, and to chase me from you, his messenger, shall not preserve you from trouble, but shall bring you into it: for God shall send you ministers that shall neither fear burning or banishment. I have offered you the word of salvation; with the hazard of my life I have remained among you: now ye yourselves refuse me, and I must leave my innocency to be declared by my God. If it be long prosperous with you, then I am not led by the spirit of truth; but if unlooked for trouble comes upon you, acknowledge the cause, and turn to God, who is gracious and merciful; but if you turn not at the first warning, he will visit you with fire and sword."