Midrasch zu Bereschit 15:10

The R. Nahman BeRabbi said: Observe what is written in this verse: Thou shalt surely give him, and thy heart shall not be grieved when thou givest unto him; of this thing the Lord thy God will bless thee in all thy work (Deut. 15:10). It does not say “for the sake of,” “on account of,” “in consequence of,” or “instead of,” but simply because of this I have made you rich and him poor. But if you do not give to him, I will reverse the wheel of fortune and make you poor and him rich. Why is that? Because God is judge; He putteth down one, and lifteth up another (Ps. 75:8).

Rabbi Joshua said: Abraham took his sword and divided them, each one into two parts, as it is said, "And he took him all these, and he divided them in the midst" (Gen. 15:10). Were it not for the fact that he divided them, the world would not have been able to exist, but because he divided them, he weakened their strength, and he brought each part against its corresponding part, as it is said, "And he laid each half over against the other" (ibid.). And the young pigeon he left alive, as it is said, "But the bird he divided not" (ibid.). Hence thou mayest learn that there was not any other bird there except a young pigeon. The bird of prey came down upon them || to scatter them and to destroy them. "The bird of prey" is nought else but David, the son of Jesse, who is compared to a "speckled bird of prey," as it is said, "Is mine heritage unto me as a speckled bird of prey?" (Jer. 12:9).

“…and he made for his father a mourning of seven days.” (Bereshit 50:10) Why do we mourn for seven days in parallel to the seven days of feasting? The Holy One said to them: in this world you shared the pain of this righteous one and mourned for him seven days, in the coming world I will transform that mourning to joy, as it says “…and I will turn their mourning into joy and will comfort them and make them rejoice from their sorrow.” (Yirmiyahu 31:12) And just as I console you, so I will console Zion and all her waste places in the manner that it says,” For the Lord shall console Zion, He shall console all its ruins, and He shall make its desert like a paradise and its wasteland like the garden of the Lord; joy and happiness shall be found therein, thanksgiving and a voice of song.” (Yeshayahu 51:3)[Alternate transaltion: “…and he made for his father a mourning of seven days.” (Genesis 50:10) Why do we mourn for seven days? In parallel to the seven days of feasting. The Holy One said to them: in this world you shared the pain of this righteous one and mourned for him seven days, in the coming world I will transform that mourning to joy, as it says “…and I will turn their mourning into joy and will comfort them and make them rejoice from their sorrow.” (Jeremiah 31:12) And just as I console you, so I will console Zion and all her waste places in the manner that it says,” For the Lord shall console Zion, He shall console all its ruins, and He shall make its desert like a paradise and its wasteland like the garden of the Lord; joy and happiness shall be found therein, thanksgiving and a voice of song.” (Isaiah 51:3)]