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 complement. Rather, knowing that the Pharisee sect desperately researched the Scriptures every day 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 the eyes but through believing with the heart.
Jesus discounted intellectual understanding while augmenting the value of faith by mirroring the faith of the Israelites who looked to Moses' snake on a pole for healing with the faith of believers who looked to Jesus' crucifixion on the cross for salvation.
Following this revelation, comes the verse that is chock full of solid theology including God's demonstration of unmerited love by giving and the sinner's salvation attained through belief, that results in his or her eternal life.
John 3:16 in Twenty-Seven Different Languages