9 Would you see yet more surely that some are saved by others' faith? Lazarus died: one day had passed, and a second, and a third: his sinews were decayed, and corruption was preying already upon his body. How could one four days dead believe, and entreat the Redeemer on his own behalf? But what the dead man lacked was supplied by his true sisters. For when the Lord had come, the sister fell down before Him, and when He said, Where have you laid him? and she had made answer, Lord, by this time he stinks; for he has been four days dead, the Lord said, If you believe, you shall see the glory of God; as much as saying, Supply thou the dead man's lack of faith: and the sisters' faith had so much power, that it recalled the dead from the gates of hell.
Have then men by believing, the one on behalf of the other, been able to raise the dead, and shall not thou, if you believe sincerely on your own behalf, be much rather profited? Nay, even if you be faithless, or of little faith, the Lord is loving unto man; He condescends to you on your repentance: only on your part say with honest mind, Lord, I believe, help thou mine unbelief. But if you think that thou really art faithful, but hast not yet the fullness of faith, thou too hast need to say like the Apostles, Lord, increase our faith: for some part you have of yourself, but the greater part you receive from Him.
Source: Catechetical Lectures (New Advent)