Behold... lo. Figure of speech Asterismos (App-6).
heir. Hebrew. inherits me. Figure of speech Metonymy (of Subject). This was strictly in accordance with 191 of the Code of Kharnmurabi. See App-15.
Related Commentaries of Genesis 15:3
Genesis 15:3
3 And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir.