14 “Jesus says unto her, Your brother shall rise again.” This was ambiguous. For He said not, Even now I will raise your brother; but, “Your brother shall rise again. Martha says unto Him, I know that he shall rise again in the resurrection, at the last day.” Of that resurrection I am sure, but uncertain about this. “Jesus says unto her, I am the resurrection.” You say, My brother shall rise again at the last day: true; but by Him, through whom he shall rise then, can he rise even now, for “I,” He says, “am the resurrection and the life.”
Give ear, brethren, give ear to what He says. Certainly the universal expectation of the bystanders was that Lazarus, one who had been dead four days, would live again; let us hear, and rise again. How many are there in this audience who are crushed down under the weighty mass of some sinful habit! Perhaps some are hearing me to whom it may be said, “Be not drunk with wine, wherein is excess;” and they say, We cannot. Some others, it may be, are hearing me, who are unclean, and stained with lusts and crimes, and to whom it is said, Refrain from such conduct, that you perish not; and they reply, We cannot give up our habits. O Lord, raise them again. “I am,” He says, “the resurrection and the life.” The resurrection because the life.
Source: Tractates on the Gospel of John (New Advent)