Here is a quote of Saint Bernard's Fifth Advent Sermon on the Three Advents.
"We know that the coming of the Lord is threefold: the third coming is between the other two and it is not visible in the way they are. At his first coming the Lord was seen on earth and lived among men, who saw him and hated him.
"At his last coming All flesh shall see the salvation of our God, and They shall look on him whom they have pierced. In the middle, the hidden coming, only the chosen see him, and they see him within themselves; and so their souls are saved. The first coming was in flesh and weakness, the middle coming is in spirit and power, and the final coming will be in glory and majesty.
"This middle coming is like a road that leads from the first coming to the last. At the first, Christ was our redemption; at the last, he will become manifest as our life; but in this middle way he is our rest and our consolation.
"If you think that I am inventing what I am saying about the middle coming, listen to the Lord himself: If anyone loves me, he will keep my words, and the Father will love him, and we shall come to him. Elsewhere I have read: Whoever fears the Lord does good things. - but I think that what was said about whoever loves him was more important: that whoever loves him will keep his words.
"Where are these words to be kept? In the heart certainly, as the Prophet says I have hidden your sayings in my heart so that I do not sin against you. Keep the word of God in that way: Blessed are those who keep it.
"Let it penetrate deep into the core of your soul and then flow out again in your feelings and the way you behave; because if you feed your soul well it will grow and rejoice. Do not forget to eat your bread, or your heart will dry up. Remember, and your soul will grow fat and sleek.
"If you keep God's word like this, there is no doubt that it will keep you, for the Son will come to you with the Father: the great Prophet will come, who will renew Jerusalem, and he is the one who makes all things new. For this is what this coming will do: just as we have been shaped in the earthly image, so will we be shaped in the heavenly image.
"Just as the old Adam was poured into the whole man and took possession of him, so in turn will our whole humanity be taken over by Christ, who created all things, has redeemed all things, and will glorify all things"