Jesus used the mustard seed — tiny, yet growing into a great plant — to picture both the kingdom of God and faith. Faith the size of a mustard seed, he said, could move mountains.
The mustard seed teaches that size is not the measure of significance. God delights to begin small and grow great things, and even the smallest genuine faith is powerful in his hands.
The Mustard Seed in Scripture
And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you.