The phrase "you of little faith" appears as just one word in Greek: oligopistos (singular, oligopistov) and oligopistoi (plural, oligopistoi). The word appears in Matthew five times: 6:30, 8:26, 14:31, 16:8. In Mt. 17:20, one finds the cognate "smallness of faith", oligopistis (in context, appearing in the accussative on account of the preceding dia, hence, oligopistian). In Luke 12:28, the word oligopistoi appears in a saying that the Lucan gospel shares with Matthew's. The word then is characteristically Matthaean, appearing not only in sayings but also in narratives.
It must be noticed that in all occurences of the word and its cognate (17:20), Jesus uses it for his disciples. The opposite of the word -- "great faith" -- is used to describe the faith of a centurion (8:5-13) and that of a Canaanite woman (15:21-28).
In Matthew 6:30, the word is used to chide the disciples who are admonished to trust in the Father in heaven and not to worry about clothes and food. In Matthew 8;26, it describes the disciples who were cowardly (deiloi, but translated as "terrified" or "frightened") during the upheaval (Matthew uses the word seismov, and not lailaq as does Mark)at sea. While the parallel passage in Mark Jesus says "Why were you afraid? Have you no faith yet?", in Matthew, Jesus rebukes them: "Why are you terrified, O you of little faith?". An echo of this is found in 14:31, an incident which involves Simon Peter (cf. 14:22-23). After Simon begins to walk on the waters he began to be frightened and so began to sink. Jesus, catching him by the hand says: "O you of little faith, why did you doubt?" Finally, in 16:8 the word is used to describe the disciples who, after witnessing the miracle of the loaves, still misunderstand the saying about the yeast of the Pharisees and Sadducees. In 17:20, the cognate word oligopistiv denotes the reason behind the failure of the disciples to cast away the demon assailing a boy.
"You of little faith" is contrasted with those whom Jesus praises for their great faith. The centurion didn't find distance a problem; he believed in Jesus' word just as a soldier would his commander's orders. "Say the word and my servant will be healed." The Canaanite woman didn't find the refusal of Jesus to her request a problem, nor did she stop believing when the refusal has become an insult. The barriers here were distance and ritual cleanliness (centurion) on the one hand, and ethnic and religious differences (Canaanite woman) on the other. But both the centurion and the woman touched Jesus with their faith inspite of the obstacles.
With the disciples, there was no question of barriers but of putting their trust and confidence in the person of Jesus. That faith is no different from the faith required from the Israelites journeying through the desert under Yahweh's guidance. "You of little faith" then is the description of those who should be trusting in the Lord but whose faith is not deep enough. This is clear in three instances where the word appears with "worry" and "anxiety" (6:25-34), "be cowardly" (8:23-27) and "to doubt" (14:22-23).
The verb for "to worry" or "be anxious" is merimnaw merimnaw which is often with a negative connotation as showing lack of confidence and a divided heart (cf. the sayings in 1 Cor. 7:32.33.34). Martha's worry about so many things is contrasted with Mary's attention to the Lord in Luke 10:41. Only in 1 Cor. 12:25 and Phil. 2:20 do we find a positive meaning for merimnaw, where it denotes the sollecitude of the members of the Body of Christ for each other. Outside of these two latter cases, "to worry" is to have a heart that is divided, inattentive to the Word and lost in "many things".
The adjective for "cowardliness" is deilov and is the opposite of the boldness and courage of those who truly have faith. It appears only two other times, in the parallel passage in Mark 4:40 and in Rev. 21:8 where those who are candidates for the lake of fire (the second death) are enumerated. In this latter, the cowardly are ranged together with the unbelieving, the vile, the murderers, etc.
The verb for "to doubt" is distazw distazw which appears one other time in Matthew and the rest of the NT. In 28:27 one finds the last description Matthew gives about the disciples: "When they saw him (the Risen Lord), some worshipped but some others doubted..." Here too, it means lack of confidence in the person and claim of Jesus about himself.
