Ambrose of Milan — as excerpted in the Catena Aurea on Luke 9:28-31

“But Matthew and Mark have related that He took them with Him after six days, of which we may say after 6000 years, (for a thousand years in the Lord’s sight are as one day;) but more than 6000 years are reckoned. We had rather then take the six days symbolically, that in six days the works of the world were completed, that by the time we may understand the works, by the works the world. And so the times of the world being finished, the resurrection to come is declared; or because, He who has ascended above the world, and has passed beyond the moments of this life, is waiting, seated as it were on a high place, for the everlasting fruit of the resurrection.”