“Behold! The proud! Their “spirit” is not right in them, but the righteous live by their faithfulness.” Habakkuk 2:4 (NRSV-CMR adapted)
The righteous live by their faithfulness. In other words, faithfulness is a way of life. In Hebrew, the term “faithful” comes from the root meaning to be true, upright, firm and steadfast-much as a strong column supports a building without moving or wavering. The notion of the righteous living by faith is core to living out the gospel message. As Paul says in Romans 1:17, “For in it [the gospel] a righteousness of God is revealed through faith for faith; as it is written, 'The one who is righteous will live by faith.'” (quoting from Habakkuk).
The question is, “How does one live by faith?” Or, “How do we become more faithful?” Reading Habakkuk in conversation with the parable of the mustard seed (Matthew 13:31-32) provides some insight.
In Habakkuk, the righteous who live by faith are contrasted with the proud (or the swollen). The proud do not have a right spirit, but are always running after “more.” Like “Death” and “the grave” they never have enough. They are bloated, malcontent, never satisfied, and swollen from their efforts. By contrast, the righteous life simply. They trust that God will provide, they don't run after things as if the ability to live depends solely on what they can amass. The righteous, live day after day simply being faithful.
A picture of the faithful is given in Jesus' teaching about the mustard seed. It is a small seed, but once planted it continues to grow, little by little, each day until it becomes a large tree. It runs after nothing. It is anxious about nothing. It simply lives, growing as it is designed to grow, being faithful. The mustard seed, unlike the 'swollen' is not anxious about its height or its end state. The mustard seed is not anxious about growing, it simply does what it is supposed to do.
How do we become more faithful? By be faithful each day. By not 'trying' to 'be something' or 'be someone' but simply do what we know to do, be who we are designed to be, each day. Like the mustard seed, we will grow in to a tower of faithfulness.