2. Does sickness come always and exclusively from the devil, as some say?
No, sickness does not come always from the devil, because in some cases is sent by God. Let’s look at some biblical examples of people who were struck by God with a disease.
Miriam, the sister of Moses, with leprosy because she spoke against Moses, as
it is written: “And Miriam and Aaron spake against Moses because of the
Ethiopian woman whom he had married: for he had married an Ethiopian woman.
And they said, Hath the LORD indeed spoken only by Moses? hath he not spoken
also by us? And the LORD heard it. (Now the man Moses was very meek, above
all the men which were upon the face of the earth.) And the LORD spake
suddenly unto Moses, and unto Aaron, and unto Miriam, Come out ye three unto
the tabernacle of the congregation. And they three came out. And the LORD
came down in the pillar of the cloud, and stood in the door of the tabernacle,
and called Aaron and Miriam: and they both came forth. And he said, Hear now
my words: If there be a prophet among you, I the LORD will make myself known
unto him in a vision, and will speak unto him in a dream. My servant Moses is
not so, who is faithful in all mine house. With him will I speak mouth to
mouth, even apparently, and not in dark speeches; and the similitude of the
LORD shall he behold: wherefore then were ye not afraid to speak against my
servant Moses? And the anger of the LORD was kindled against them; and he
departed. And the cloud departed from off the tabernacle; and, behold, Miriam
became leprous, white as snow: and Aaron looked upon Miriam, and, behold, she
was leprous. And Aaron said unto Moses, Alas, my lord, I beseech thee, lay
not the sin upon us, wherein we have done foolishly, and wherein we have
sinned. Let her not be as one dead, of whom the flesh is half consumed when
he cometh out of his mother's womb. And Moses cried unto the LORD, saying,
Heal her now, O God, I beseech thee. And the LORD said unto Moses, If her
father had but spit in her face, should she not be ashamed seven days? let
her be shut out from the camp seven days, and after that let her be received
in again. And Miriam was shut out from the camp seven days: and the people
journeyed not till Miriam was brought in again” (Numbers 12:1-15). That it
was God who struck Miriam with leprosy is confirmed by God in these terms:
“Remember what the LORD thy God did unto Miriam by the way, after that ye
were come forth out of
God struck king Uzziah with leprosy because his heart was lifted up and he was unfaithful to God. Here is what the Scripture says: “But when he was strong, his heart was lifted up to his destruction: for he transgressed against the LORD his God, and went into the temple of the LORD to burn incense upon the altar of incense. And Azariah the priest went in after him, and with him fourscore priests of the LORD, that were valiant men: And they withstood Uzziah the king, and said unto him, It appertaineth not unto thee, Uzziah, to burn incense unto the LORD, but to the priests the sons of Aaron, that are consecrated to burn incense: go out of the sanctuary; for thou hast trespassed; neither shall it be for thine honour from the LORD God. Then Uzziah was wroth, and had a censer in his hand to burn incense: and while he was wroth with the priests, the leprosy even rose up in his forehead before the priests in the house of the LORD, from beside the incense altar. And Azariah the chief priest, and all the priests, looked upon him, and, behold, he was leprous in his forehead, and they thrust him out from thence; yea, himself hasted also to go out, because the LORD had smitten him. And Uzziah the king was a leper unto the day of his death, and dwelt in a several house, being a leper; for he was cut off from the house of the LORD: and Jotham his son was over the king's house, judging the people of the land” (2 Chronicles 26:16-21).
God struck king Jehoram with an incurable disease because of his wickedness, as it is written: “And after all this the LORD smote him in his bowels with an incurable disease. And it came to pass, that in process of time, after the end of two years, his bowels fell out by reason of his sickness: so he died of sore diseases. And his people made no burning for him, like the burning of his fathers” (2 Chronicles -19).
As you can see, in the above mentioned cases sickness was a judgement sent by God upon some people to punish them for their transgressions. Therefore those who claim that all those believers who are sick have been struck by the devil, as the righteous Job was struck by the devil with painful boils from the sole of his foot to the crown of his head (Job 2:7), lie against the truth.
Of course, there are many cases in which it is the devil who strikes believers with a disease because God allows the devil to strike believers with a particular disease to test them or to prevent them from becoming conceited, but there are also cases in which the disease is a judgement of God or a punishment inflicted by God on believers because they have despised His Word by doing what is evil in His eyes.