2 Ne 1:29 But if ye will not hearken unto him I take away my first blessing

The blessing and birthright were traditionally given to the oldest son under the patriarchal order. This practice was modified at times in particular situations:

“A patriarch could bless his offspring by calling upon the powers of heaven. As he gave the birthright blessing to one of his sons, for instance, the keys and powers of the priesthood were extended to the next generation. In the patriarchal order, under the law of primogeniture, these priesthood rights normally were to be given to the eldest son.” (D. Ludlow, Encyclopedia of Mormonism, p. 1138)

Bruce R. McConkie

“Lineage alone does not guarantee the receipt of whatever birthright privileges may be involved in particular cases. Worthiness, ability, and other requisites are also involved. Jacob prevailed over his older brother Esau because ‘Esau despised his birthright.’ (Gen. 25:24-34;  27; Rom. 9:10-12.) The Lord placed Ephraim (the younger) before Manasseh to fulfil his own purposes (Gen. 48); and Nephi, junior in point of birth to Laman and Lemuel, was made a ruler and a teacher over them, a circumstance that became the cause of much contention for many generations. (1 Ne. 2:22; 16:37-38; 18:10; 2 Ne. 5:3;  19; Mosiah 10:11-17.)” (Mormon Doctrine, p. 88)