When Abram was ninety-nine years old YHWH appeared to Abram and said to him, "I am El Shaddai; walk before me, and be blameless..."
Genesis 17:1

This is the first use in the Bible of the name El Shaddai for God. People have long disagreed over what it means, but most now believe that it probably means "God of the Mountain".

God told Abraham to walk before him and be perfect. Nobody is perfect, not even Abraham, but Paul gave these same instructions in his letters. It's more about being wholehearted then being flawless.