Musar zu Bereschit 15:3

In order to appreciate the dimension of holiness Isaac represented, it is fitting that we first see what the Zohar says on the subject of the עקדה. When Abraham was about to slaughter Isaac, the latter's soul flew away to be replaced later by a holy spirit from the Celestial Regions. It follows then that Isaac's life after the עקדה, was the life of a human being who had not originated from a drop of semen. We must view Isaac as someone re-born in consequence of that experience: a totally new creature. G–d had applied the strictest yardstick to him by letting him die, and subsequently by infusing him with a new soul. He had also sanctified his body; from that time on Isaac's body resembled that of אדם הראשון, also not the product of a drop of semen. Now we understand also why the ram which Abraham sacrificed in lieu of Isaac was not the product of natural procreation, i.e. through semen, but was created during the period of dusk on the sixth day of Creation as reported in Avot 5,6. When Genesis 22,13 describes this ram as והנה איל אחר נאחז וכו' "and here a ram after was caught, etc.," this means that this ram was created after all the other mammals had already been created and had procreated. The word אחר therefore is to be understood in the same sense as the same word when Abraham said to the angels אחר תעבורו. Isaac teaches us about G–d's very first objective when He set out to create this universe which would develop to become as perfect as He envisaged it.