How he sware unto the LORD, [and] vowed unto the mighty [God] of Jacob;
Ver. 2. How he sware unto the Lord] Out of the abundance of his affections, 1 Chronicles 29:3, see Psa 119:106 he solemnly took God to witness; and this he did, say the Rabbis, at that time when he saw the punishing angel, and was terrified.
And vowed unto the mighty God of Jacob] Jacob is mentioned, say the Hebrews, Quia primo vovit. because he first vowed to God, Genesis 28:20, whence he is called, Pater votorum, the Father of vows (Kimchi, Aben Ezra).