The so-called "Prince of Preachers" was Charles Spurgeon. It's always a mistake to read a sermon by Spurgeon the day before you are supposed to preach on the same text. I should just throw out my sermon, apologize to my congregation for being lame, and read Spurgeon's sermon on Mark 4:26-29.
In this particular sermon, after exhorting us to "sow the Word" every chance we get, Spurgeon reminds us the growth comes from God.
See what he preached regarding this text:
Mark 4:26-29 And he said, “The kingdom of God is as if a man should scatter seed on the ground. He sleeps and rises night and day, and the seed sprouts and grows; he knows not how. The earth produces by itself, first the blade, then the ear, then the full grain in the ear. But when the grain is ripe, at once he puts in the sickle, because the harvest has come.”
"Let us now think of what you cannot do. You cannot, after the seed has left your hand, cause it to put forth life. I am sure you cannot make it grow, for you do not know how it grows. The text saith, "And the seed should spring and grow up, he knoweth not how." That which is beyond the range of our knowledge is certainly beyond the reach of our power. Can you make a seed germinate? You may place it under circumstances of damp and heat which will cause it to swell and break forth with a shoot, but the germination itself is beyond you. How is it done? We know not. After the germ has been put forth, can you make it further grow, and develop its life into leaf and stem? No; that, too, is out of your power. And when the green, grassy blade has been succeeded by the ear, can you ripen it? It will be ripened; but can you do it? You know you cannot; you can have no finger in the actual process, though you may promote the conditions under which it is carried on.
Life is a mystery; growth is a mystery; ripening is a mystery: and these three mysteries are as fountains sealed against all intrusion. How comes it that there is within the ripe seed the preparations for another sowing and another growth? What is this vital principle, this secret reproducing energy? Knowest thou anything about this? The philosopher may talk about chemical combinations, and he may proceed to quote analogies from this and that; but still the growth of the seed remains a secret, it springs up, he knoweth not how. Certainly this is true of the rise and progress of the life of God in the heart. It enters the soul, and roots itself we know not how. Naturally men hate the word, but it enters and it changes their hearts, so that they come to love it; yet we know not how. Their whole nature is renewed, so that instead of producing sin it yields repentance, faith, and love; but we know not how.
How the Spirit of God deals with the mind of man, how he creates the new heart and the right spirit, how we are begotten again unto a lively hope, we cannot tell. The Holy Ghost enters into us; we hear not his voice, we see not his light, we feel not his touch; yet he worketh an effectual work upon us, which we are not long in perceiving. We know that the work of the Spirit is a new creation, a resurrection, a quickening from the dead; but all these words are only covers to our utter ignorance of the mode of his working, with which it is not in our power to meddle. We do not know how he performs his miracles of love, and, not knowing how he works, we may be quite sure that we cannot take the work out of his hands. We cannot create, we cannot quicken, we cannot transform, we cannot regenerate, we cannot save."
Spurgeon's full sermon "What the farm laborers can do and what they cannot do" can be found here.