2 And when he had fasted forty days and forty nights, he was afterward an hungred.
Matthew 4:2 King James Version (KJV)
Hunger leaves you doing the first week of fasting and what remains is habit hunger.
“When true hunger returns after around forty days, more or less, of fasting, starvation begins.” The Fasting Prayer by Franklin Hall pg. 143
3 And when the tempter came to him, he said, If thou be the Son of God, command that these stones be made bread.
Matthew 4:3 King James Version (KJV)
Breaking A long or complete (one when hunger returns) fast hastily can be harmful to you and even deadly. You must take your time to return to normal eating habits your stomach is like that of a baby. The fast here was already finished Jesus was being tempted to break the fast poorly which could result in sickness or death.
8 Again, the devil took him to a very high mountain and showed him all the kingdoms of the world and their splendor.
9 “All this I will give you,” he said, “if you will bow down and worship me.”
10 Jesus said to him, “Away from me, Satan! For it is written: ‘Worship the Lord your God, and serve him only.’”
Matthew 4:8-10 (NIV)
If Satan can give Jesus all the kingdoms of the world and their splendor that shows he is the ruler/king of this world.