#preaching

Hey everyone hope you are all doing well. Was struck recently when reading about Spurgeon, that he was said to preach between 4-10 times a week. Murray's biography of Dr Martyn Lloyd Jones suggested that he preached on average 4-5 sermons a week, and it was said of Calvin that he preached twice...

May God grant us a blessed Lord's day, brethren. May any Christian (man?) teach under certain circumstances? I know a common opinion in Reformed circles is only people called to offices of teaching ought to teach. Is it so? How can we prove that it is or isn't based on God's word? If it is...