User blog comment:Kajune/Lucifer, first son?/@comment-3045936-20160408173312/@comment-1149167-20160408175335

The quote from Supernatural Super Wiki.

"As God's favorite, His first son, you may be the one thing in all of creation that He still cares about. The one thing that could finally make Him show Himself, so I can confront Him and He can acknowledge the wrongs He's done me."

While Lucifer may have been first in his Father's affection, it has been previously established (5.10 Abandon All Hope..., 5.22 Swan Song) that Michael was the eldest archangel, and Lucifer was his younger brother.