(Canto 4, lines 55-60)
"The First Parent" is Adam. Abel, Adam's second son, was a shepherd, while his brother Cain was a farmer. Both of them presented their offerings to God, but only Abel's offerings pleased Him. Out of envy, Cain killed Adam (as described in Genesis 4:1-8), which is why the Comedy describes Abel as saved from Hell by Jesus, while Cain was condemned to the ninth circle of Hell, to which he lends his name, "Caïna".
Noah was a descendant of Adam's third son Seth, described as a honest man without faults. When God witnessed the incurable state of sin among the people of the world he was so angered that he planned on letting the whole world perish in a giant flood, but then ordered Noah to build an ark and let his family escape the catastrophe. (Chapters 5-10 of Genesis).
Abram, a descendant of Noahs eldest son Sem, was given the name "Abraham" by God, as described in chapters 11-17 of Genesis, wherein it is said (Genesis 17:5): "the Lord appeared unto Abram, and said unto him ... Neither shall thy name any more be called Abram, but thy name shall be Abraham; for a father of many nations have I made thee." Thus he is here referred to as "patriarch", and even today are the religions of Judaism, Christianity and Islam together labelled as "Abrahamic" religions. He is also called "the obedient" here, because of his willingness to sacrifice his son Isaac on the command of God - who, however, interfered at the last moment and let Isaac live. (Genesis chapter 22)
David was an 11th/10th century BC king of Israel and Judah. According to conventional dating he succeeded Saul (who had repeatedly conspired against him) as king of Israel in 1003 BC. David was the seventh and youngest son of Jesse of Bethlehem and rose to prominence after slaying the giant Goliath in a battle against the Philistines. After occupying Jerusalem, he made the city into his capital and ruled from there for thirty years. David is credited with making improvements to the harp and turning music into an important part of the Jewish sacrifice, and also as the author of the 150 Psalms (see 1, 2 Samuel).
Rachel was the second daughter of Jacob's uncle Laban. Jacob came to him after his father had sent him away to find a wife. When he met Rachel, he immediately fell in love with her. Laban agreed to his proposal and promised to wed Rachel to him if he would work for him seven years. But after toiling seven years to receive Rachel as his bride, Laban gave him Rachel's sister Leah as wife instead, on the grounds that a younger sister cannot be married before an older. However, he would agree to Rachel marrying him seven days after Leah, but only if Jacob would work for him seven more years. In total, Jacob therefore came to work fourteen years for Laban. (Genesis 28, 29).