Are we obligated to inform new believers about potentially losing their newly acquired salvation?

[bling]

Esau had no say in the order of birth, so I would say that Esau did not truly have any right to sell his birthright.

The Bible says he sold his birthright.

 

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Esau sells his birthright and loses the blessing, and all goes to Jacob and this according to the predetermination of God before they were born.
Same thing today for all people, is what is predestined to occur. God did not make Esau sin, or make him a profane fornicator.
Esau just was by his nature those things, and that this was predetermined so that God's calling according to His electing people would remain true.
Frankly it is written down for us as an example that the calling of God overrides the natural perceived order of things as man thinks they are done. God is in charge of the affairs of all creation and He demonstrates His power in the earth over the creation.

Did God "predestine" Jacob to lie and stile Esau's blessing?

 

[sdowney717]

Did God "predestine" Jacob to lie and stile Esau's blessing?

Good question, maybe God predestined Rebecca to influence Jacob to do those things.
Gen 27
5 Now Rebekah was listening when Isaac spoke to Esau his son. And Esau went to the field to hunt game and to bring it. 6 So Rebekah spoke to Jacob her son, saying, “Indeed I heard your father speak to Esau your brother, saying, 7 ‘Bring me game and make savory food for me, that I may eat it and bless you in the presence of the Lord before my death.’ 8 Now therefore, my son, obey my voice according to what I command you. 9 Go now to the flock and bring me from there two choice kids of the goats, and I will make savory food from them for your father, such as he loves. 10 Then you shall take it to your father, that he may eat it, and that he may bless you before his death.”

Now Esau also troubled both his parents a lot, so I can see why Rebecca would desire Jacob to inherit and not Esau.
Rebecca knowing Isaac was old and maybe she thought him to be somewhat crazy decided to do something and it had to be quick.

Gen 26
34 When Esau was forty years old, he took as wives Judith the daughter of Beeri the Hittite, and Basemath the daughter of Elon the Hittite. 35 And they were a grief of mind to Isaac and Rebekah.

Esau married what would be considered idol worshippers, for Esau was a profane person and had no regard for God. So Esau's lineage would become the enemies of Israel and God. Esau's decision to do that comes before Jacob buys his birthright and before Jacob inherits his blessing. Esau shows how he cares nothing for his parents or God.