Faith as a grain of mustard seed.
A quote from the Early Church Fathers: Jerome (347-420 AD)
“The man who sows in his field is interpreted by many as the Saviour. He sows in the souls of believers. By others, he is interpreted as one who sows in his field – that is to say, in himself and in his heart. Who is it that sows if not our mind and heart? They take up the grain of preaching and nurture the plant with the moisture of faith, making it sprout and shoot up in the field of the heart. The preaching of faith in the gospel appears to be least among all tasks. Indeed, anyone who preaches the God-man of truth, Christ who died, and the stumbling block of the cross may not think immediately of mere faith as the primary doctrine. Put this particular doctrine side by side with the teachings of the philosophers, their books, their splendid eloquence and fine discourses, and you will see just how small it is compared with the other seeds of the gospel plant. When those teachings grow, they have nothing to show that is pungent or vigorous or vital. Everything turns out weak and withering in a plant and in herbs that quickly dry up and fall to the ground. But when this tiny gospel teaching that seemed insignificant at the beginning has been planted either in the soul of the believer or throughout the world, it does not turn out to be just a plant. It grows into a tree, so that the birds of the air, which we interpret as the souls of believers or deeds dedicated to the service of God, come and dwell on its branches.” (excerpt from COMMENTARY ON MATTHEW 2.13.31)