Jesus said, “No one has ascended into heaven but He who descended from heaven, the Son of man. And as Moses lifted up the serpent in the wilderness, so must the Son of man be lifted up, that whoever believes in Him may have eternal life.” For God so loved the world that He gave his only Son, that whoever believes in Him should not perish but have eternal life. For God sent the Son into the world, not to condemn the world, but that the world might be saved through Him.”
John 3: 13-17 (Gospel Reading for Sunday Before the Holy Cross)
I have often been asked “What do I need to believe in order to be a Christian?” The answer for what you have to believe is very simple.
  1. God (not us, not a big bang, not a random act) created the world and He created it perfect. (Genesis 1)
  2. The world fell through sin. (Genesis 3)
  3. The word has been redeemed through the saving work of Jesus Christ. (John 3:16)
It is very simple. God created us perfect. We human beings messed up the perfect creation. And God gave us a chance to find the original perfection through the attaining of salvation. Salvation is our work in this life and our destination for eternal life (if we do the “work” in this life).
The Gospel passage from today is a few verses of a long discourse that Jesus had with Nicodemus, a Pharisee, who came to Him privately to ask Him some questions. This passage was not addressed to a large group of people, as many of Jesus’ discourses were. In this short passage, Jesus tells Nicodemus that “no one has ascended into heaven but He who descended from heaven, the Son of Man.”  He doesn’t reveal Himself as the Son of Man, but teaches Nicodemus, an obviously educated Jewish leader, in a way that no one had ever taught him. As Jesus often did, His insight opened up deeper dialogue, which led to deeper curiosity, which led people to believe in Him.
Jesus continued by referencing the Old Testament book of Numbers, Chapter 21: 4-9
From Mount Hor they set out by the way to the Red Sea, to go around the land of Edom; and the people became impatient on the way. And the people spoke against God and against Moses, “Why have you brought us up out of Egypt to die in the wilderness? For there is no food and no water, and we loath this worthless food.” Then the Lord sent fiery serpents among the people, and they bit the people, so that many people of Israel died. And the people came to Moses and said, “We have sinned, for we have spoken against the Lord and against you; pray to the Lord, that He take away the serpents from us.” So Moses prayed for the people. And the Lord said to Moses, “Make a fiery serpent, and set it on a pole; and everyone who is bitten, when he sees it, shall live.” So Moses made a bronze serpent, and set it on a pole; and if a serpent bit any man, he would look at the bronze serpent and live.
(In case you were wondering, this is where the medical symbol with the serpents comes from, as well as the Orthodox bishop’s staff having two serpents at the top of it.)
Jesus compared Himself (again in a hidden way) to the bronze serpent that Moses lifted up in the wilderness, which brought healing to all who looked upon it. Jesus said that “the Son of Man” (Him) would also be lifted up, (referring to being lifted up on the cross) that whoever believed in Him would not have only healing but eternal life.
John 3:16 is the most succinct summary of salvation:  For God (the creator) so loved the world (even when it went away from Him through sin) that He gave His only Son, that whoever believe in Him should not perish but have eternal life.
He continues that the purpose of the Son coming into the world was not to judge the world but to save the world.
Now, there is one “condition” for us, in order for God’s plan in sending His Son into the world to save the world to be fulfilled. And that is we need to believe. Many people miss that world. They read John 3:16 in this way: For God so loved the world that He gave His only Son, that whoever merely lives and breathes for a while should not perish but have eternal life.” This is obviously not what the passage says. We are, however, called to do more than live and breathe for a little while in order to attain salvation. We have to believe. What we believe is not limited to words but also involves actions, it requires not only hearing but DOING something.
As for the question “What do I need to do in order to attain salvation?” the answer there is a combination of your faith (love God), your works (love your neighbor) and God’s grace and mercy. 
Long ago, Moses prefigured Your precious Cross in himself, and he defeated Amalek and put them to flight. And David, that musician, called it a footstool and decreed that we worship You there, O Christ God. Today, as we sinners with unworthy lips kiss the Cross and worship You, Who accepted to be nailed to it, we extol You and pray: Lord, as You did for the Robber, count us worthy of Your Kingdom. (Doxastikon, Great Vespers of Holy Cross, Trans. by Fr. Seraphim Dedes)
Christ didn’t come to judge us, but to save us. But we have a part to play in that as well. Play your part today!