The most concise presentation of the "Gospel" in one verse is found in John 3:16.
Ruling Pharisee Nicodemus secretly came to Jesus in the night to affirm his opinion that Jesus was God's messenger, but he obviously did not believe that Jesus was God Himself. He was probably hoping to more accurately pinpoint Jesus' identity, purpose, and the source of His miracle working power.
Jesus, to avoid this ill-conceived trap did not respond to Nicodemus' weak compliment. Rather, knowing that being a Pharisee he certainly researched the Scriptures every day with all diligence to determine when and how God would restore His kingdom, Jesus got right to the point by challenging Nicodemus' flawed theology. Jesus told him that only those who experience a second birth can even see the kingdom of God.
This seemingly ridiculous requirement startled Nicodemus. Jesus explained that the Kingdom of God was spiritual not carnal (physical) and to enter into it required a spiritual birth. It cannot be accessed in the physical realm. The entrance is revealed not through seeing with his eyes but through believing within his heart.
Jesus discounted intellectual understanding by augmenting the value of believing and trusting God when he parallelled the faith of the ancient Israelites who looked to Moses' snake on a pole for healing with the faith of contemporary believers who would look to Jesus' crucifixion on the cross for their salvation.
Following this revelation, comes the verse found in John chapter three verse sixteen that is chock full of solid Biblical theology. It includes God's demonstration of unmerited love by persuing rebels so that He could offer His own life as the necessary and only acceptable atonement to appease the righteous wrath of God, and the sinner's salvation attained through his or her simple belief that this is true (causing repentance), that will result his or her gaining eternal life.
John 3:16 in Twenty-Seven Different Languages