Summary: A short but different take on the meaning of what Jesus meant when He spoke of faith like a mustard seed.
Luke 17:5 (quickview)  The apostles said to the Lord, "Increase our faith!" (6) He replied, "If you have faith as small as a mustard seed, you can say to this mulberry tree, `Be uprooted and planted in the sea,’ and it will obey you.
The apostles (the twelve) have asked Jesus to increase their faith. This request was probably brought on by the depth of forgiving that Jesus had just told them they should have in previous verses. Surely they must have felt inadequate and overwhelmed by what He had said.
He compares the faith required to a mustard seed. Let’s examine that.
Let’s view how some other translations make the statement about the mustard seed.
Jesus says to them if you had faith like a mustard seed or as a mustard seed you could achieve great things. I have to wonder why He used that example so let’s do a little investigation of the mustard seed in scripture.
First of all how does Jesus Himself use the mustard seed as an example in His other teaching? Let’s look.
Matthew 13:31 (quickview)  He told them another parable: "The kingdom of heaven is like a mustard seed, which a man took and planted in his field. (32) Though it is the smallest of all your seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds of the air come and perch in its branches."
Mark 4:30 (quickview)  Again he said, "What shall we say the kingdom of God is like, or what parable shall we use to describe it? (31) It is like a mustard seed, which is the smallest seed you plant in the ground. (32) Yet when planted, it grows and becomes the largest of all garden plants, with such big branches that the birds of the air can perch in its shade."
Luke 13:18 (quickview)  Then Jesus asked, "What is the kingdom of God like? What shall I compare it to? (19) It is like a mustard seed, which a man took and planted in his garden. It grew and became a tree, and the birds of the air perched in its branches."
Note that in these three gospels Jesus uses the tiny mustard seed to describe how the kingdom of God will grow. He said it will start from a small seed but will grow very large.
What is unusual about a mustard seed? Well, it is the smallest seed known at that time. But we know from Jesus own words that a tiny mustard seed produces tremendous growth and finally produces a tree sized plant that can reach a height of 12 feet or more and provides shade and a place that birds can perch upon.
Could it be that Jesus is here saying that if you have a faith in Him that, like the mustard seed, starts small but continues to develop until it is a large tree like plant that you will be able to say to the mulberry tree be removed from the ground and be planted in the sea? Saying perhaps that if your faith in Him begins small but continues to grow as you learn more about Him your faith in Him will become strong enough so that you will be able to do unexpected things.