Genesis 4:8-11

8 Cain said to his brother Abel, “Let’s go out to the field.”
The MT has simply “and Cain said to Abel his brother,” omitting Cain’s words to Abel. It is possible that the elliptical text is original. Perhaps the author uses the technique of aposiopesis, “a sudden silence” to create tension. In the midst of the story the narrator suddenly rushes ahead to what happened in the field. It is more likely that the ancient versions (Samaritan Pentateuch, LXX, Vulgate, and Syriac), which include Cain’s words, “Let’s go out to the field,” preserve the original reading here. After writing אָחִיו (’akhiyv, “his brother”), a scribe’s eye may have jumped to the end of the form בַּשָּׂדֶה (basadeh, “to the field”) and accidentally omitted the quotation. This would be an error of virtual homoioteleuton. In older phases of the Hebrew script the sequence יו (yod-vav) on אָחִיו is graphically similar to the final ה (he) on בַּשָּׂדֶה.
While they were in the field, Cain attacked
Heb “arose against” (in a hostile sense).
his brother
The word “brother” appears six times in vv. 8–11, stressing the shocking nature of Cain’s fratricide (see 1 John 3:12).
Abel and killed him.

9 Then the Lord said to Cain, “Where is your brother Abel?”
Where is Abel your brother? Again the Lord confronts a guilty sinner with a rhetorical question (see Gen 3:9–13), asking for an explanation of what has happened.
And he replied, “I don’t know! Am I my brother’s guardian?”
Heb “The one guarding my brother [am] I?”
Am I my brother’s guardian? Cain lies and then responds with a defiant rhetorical question of his own in which he repudiates any responsibility for his brother. But his question is ironic, for he is responsible for his brother’s fate, especially if he wanted to kill him. See P. A. Riemann, “Am I My Brother’s Keeper?” Int 24 (1970): 482-91.
10But the Lord said, “What have you done?
What have you done? Again the Lord’s question is rhetorical (see Gen 3:13), condemning Cain for his sin.
The voice
The word “voice” is a personification; the evidence of Abel’s shed blood condemns Cain, just as a human eyewitness would testify in court. For helpful insights, see G. von Rad, Biblical Interpretations in Preaching; and L. Morris, “The Biblical Use of the Term ‘Blood,’” JTS 6 (1955/56): 77-82.
of your brother’s blood is crying out to me from the ground!
11So now, you are banished
Heb “cursed are you from the ground.” As in Gen 3:14, the word “cursed,” a passive participle from אָרָר (’arar), either means “punished” or “banished,” depending on how one interprets the following preposition. If the preposition is taken as indicating source, then the idea is “cursed (i.e., punished) are you from [i.e., “through the agency of”] the ground” (see v. 12a). If the preposition is taken as separative, then the idea is “cursed and banished from the ground.” In this case the ground rejects Cain’s efforts in such a way that he is banished from the ground and forced to become a fugitive out in the earth (see vv. 12b, 14).
from the ground, which has opened its mouth to receive your brother’s blood from your hand.
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