What I love about this passage is how it appears when you read it in light of the documentary hypothesis. The DH is the current model for the authorship of the Old Testament, and attributes different sections of the first five books to the authors J, E, D, and P. The gist of the theory is that JEDP were originally separate documents/traditions that were edited together to make the text as we know it today.

If you look at Genesis 22 in this color-coded version you will find that the verse quoted by the OP is by the 'Eloist' (E), then the text is interrupted by a passage by a later editor, then it picks up with E again. If you ignore the later addition, it is obvious that the original E text had Abraham following through with the sacrifice: The angel praises Abraham for not withholding his son, he leaves with his men, and Isaac is never mentioned again.

E source:

And they came to the place which God had told him of; and Abraham built an altar there, and laid the wood in order, and bound Isaac his son, and laid him on the altar upon the wood. And Abraham stretched forth his hand, and took the knife to slay his son.

(R)edactor:

And the angel of the LORD called unto him out of heaven, and said, Abraham, Abraham: and he said, Here am I. And he said, Lay not thine hand upon the lad, neither do thou any thing unto him: for now I know that thou fearest God, seeing thou hast not withheld thy son, thine only son from me. ...

back to the E source:

And said, By myself have I sworn, saith the LORD, for because thou hast done this thing, and hast not withheld thy son, thine only son. That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies; And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice. So Abraham returned unto his young men, and they rose up and went together to Beersheba; and Abraham dwelt at Beersheba.