God's Love
Jesus was addressing Nicodemus. The love of God is the result of "that" He gave His only begotten Son, "that" whoever "believes" "in" Him shall not perish, "but" have eternal life.
John 3:16New American Standard Bible (1995)
“For God so loved the world, that He gave His only begotten Son, that whoever believes in Him shall not perish, but have eternal life.