True faith is not like a grain of sand, but like a grain of mustard seed. It is like a seed. A seed is distinguished from a grain of anything else by the fact that it has life. It is a living thing and therefore is able to germinate and grow. Becoming a Christian is not just reformation.
Man can achieve reformation.
Becoming a Christian is Christ coming to dwell within the person, bringing life where there was deadness and light where there was darkness. He makes not just a better person, but a new person. A person who is spiritually alive, who is able to believe, able as a sinner to look to Christ for salvation. Able to rejoice in the mercy of God, and in God Himself. The mustard seed must be sown in the earth before it will germinate.