Exodus 6:2 plainly states that while God appeared to Abraham, Isaac and Jacob as God Almighty (El Shaddai), he did not make himself known to them by his personal name YHWH. This confuses some readers. One asks, “Why does God say he didn’t reveal his name ‘Yahweh’, when he obviously glaringly did so in Genesis, many, many times?”
Some of the answers one gets to such a question on a public forum like Stack Exchange are truly horrendous. One respondent suggests the writer of the Exodus passage believed it, but the writer of the Genesis passages believed differently. Let’s just say the apostle Paul would beg to differ, as would the Lord Jesus.