What is the symbolic significance/inter-connection of Satan , Sin and Death ?
You should read the "themes" section at the link below for a thorough answer.
To summarize, Paradise Lost presents the Christian world view that Satan, sin and death are related. Satan was the vehicle for bringing sin into the world. In the epic poem, Satan decides to tempt Adam and Eve because he knows they are weak and will succumb to his temptations, and in this way, he can get back at God for expelling him from heaven. He cannot fight God, but he can fight God's creatures because they are not strong.
Adam and Eve were created for fellowship with God, but they have free will and choose to sin. Through Satan, then, they sin and this sin results in their death. God created them to live forever in the Garden of Eden, but sin disallowed his. God cannot exist with sin, so man's sin separated him from God.
"The wages of sin is death," says the Bible, "But the gift of God is eternal life...." God had to provide a way for man to overcome his sin, so he sent his son, Jesus Christ, to atone for the sins of mankind. In this way, the sin that separates man from God is paid for by someone else. Because of Christ's work on the cross, physical death is overcome by eternal life and "death has no more dominion" over man. Milton believed this, even though in his epic poem, there is a lot that departs from the Bible because, after all, Paradise Lost is fiction. Milton gives voice to characters in his epic that do not appear in the Bible account.