5 What is that night wherein, when it comes, no one shall be able to work? Hear what the day is, and then you will understand what the night is. But how shall we hear what the day is? Let Himself tell us: “As long as I am in this world, I am the light of the world.” See, He Himself is the day. Let the blind man wash his eyes in the day, that he may behold the day. “As long,” He says, “as I am in the world, I am the light of the world.” Then will it be night of a kind unknown to me, when Christ will no longer be there; and so no one will be able to work.
An inquiry remains, my brethren; patiently listen to me as I inquire. With you I inquire: With you shall I find Him to whom my inquiry is addressed. We are agreed; for it is expressly and definitely stated that the Lord proclaimed Himself in this place as the day, that is, the light of the world. “As long,” He says, “as I am in this world, I am the light of the world.” Therefore He Himself works. But how long is He in this world? Are we to think, brethren, that He was here then, and is here no longer?
If we think so, then already, after the Lord's ascension, did that fearful night begin, when no one can work. If that night began after the Lord's ascension, how was it that the apostles wrought so much? Was that the night when the Holy Spirit came, and, filling all who were in one place, gave them the power of speaking in the tongues of every nation? Was it night when that lame man was made whole at the word of Peter, or rather, at the word of the Lord dwelling in Peter? Was it night when, as the disciples were passing by, the sick were laid in couches, that they might be touched at least by their shadow as they passed? Yet, when the Lord was here, there was no one made whole by His shadow as He passed; but He Himself had said to the disciples, “Greater things than these shall you do.” Yes, the Lord had said, “Greater things than these shall you do;” but let not flesh and blood exalt itself: let such hear Him also saying, “Without me you can do nothing.”
Source: Tractates on the Gospel of John (New Advent)