The sun shall be turned into darkness, and the moon into blood, before that great and notable day of the Lord comes:
Read Chapter 2
Augustine of Hippo
the Church, shall be darkened, because in those tremendous temptations and tribulations which shall be in the end of the world, many who had seemed as bright and as firm as the sun and the stars shall fall from the faith.
This is believed partly as something which had been done at the Lord's passion, and partly as something to be done in the future.
This is, as if the power of Christ were hidden, or His doctrine temporarily obscured, or covered by a veil, when the servants of Antichrist are brought to attack the servants of Christ.
The Church, more than is wont, will shed her blood for Christ
this clearly describes for us the miracles that took place at the cross- the earthquake and the turbulence of the earth (Matt. 27:52), the darkness of the sun (Lk. 23:44), and the changing of the full moon into blood.
the sun shall be darkened," instead of being blackened; not disappearing, but being overwhelmed by the light of Christ’s appearance, and so too will the stars and the moon. For what need is there for sensory light when the Sun of Righteousness has appeared and night is no more?