Are you saying that God causes man to sin?
James 1:13 Let no man say when he is tempted, I am tempted of God: for God cannot be tempted with evil, neither tempteth he any man:
James 1:14 But every man is tempted, when he is drawn away of his own lust, and enticed.
James 1:15 Then when lust hath conceived, it bringeth forth sin: and sin, when it is finished, bringeth forth death.
God does not cause man to sin. Man sins because he follows, of his own will, the pattern in the verses above. First he gives into lust and enticed. When he gives into that lust, he commits sin.
When man commits sin God is not in the picture at all.
God doesn't tempt man directly. But he does send evil spirits to do it for him. They don't have to work to hard though as man is naturally evil anyway and tempts himself. A decree and temptation are two entirely different things.
1 Kings 22:19-23 ESV
19 And Micaiah said, “Therefore hear the word of the Lord: I saw the Lord sitting on his throne, and all the host of heaven standing beside him on his right hand and on his left; 20 and the Lord said, ‘Who will entice Ahab, that he may go up and fall at Ramoth-gilead?’ And one said one thing, and another said another. 21 Then a spirit came forward and stood before the Lord, saying, ‘I will entice him.’ 22 And the Lord said to him, ‘By what means?’ And he said, ‘I will go out, and will be a lying spirit in the mouth of all his prophets.’ And he said, ‘You are to entice him, and you shall succeed; go out and do so.’ 23 Now therefore behold, the Lord has put a lying spirit in the mouth of all these your prophets; the Lord has declared disaster for you.”
God also sends harmful spirits to torment people who need tormenting:
1 Samuel 16:14 ESV
14 Now the Spirit of the Lord departed from Saul, and a harmful spirit from the Lord tormented him.
The bible also records that some reject Christ as they were destined to do:
1 Peter 2:8 ESV
8 and
“A stone of stumbling,
and a rock of offense.”
They stumble because they disobey the word, as they were destined to do.
The bible clearly records that God predestined the most heinous sin in hisotry:
Acts 4:27-28 ESV
27 for truly in this city there were gathered together against your holy servant Jesus, whom you anointed, both Herod and Pontius Pilate, along with the Gentiles and the peoples of Israel, 28 to do whatever your hand and your plan had predestined to take place.
And remember God turning Job over to Satan for a time?
Job 1:6-12 ESV
6 Now there was a day when the sons of God came to present themselves before the Lord, and Satan [2] also came among them. 7 The Lord said to Satan, “From where have you come?” Satan answered the Lord and said, “From going to and fro on the earth, and from walking up and down on it.” 8 And the Lord said to Satan, “Have you considered my servant Job, that there is none like him on the earth, a blameless and upright man, who fears God and turns away from evil?” 9 Then Satan answered the Lord and said, “Does Job fear God for no reason? 10 Have you not put a hedge around him and his house and all that he has, on every side? You have blessed the work of his hands, and his possessions have increased in the land. 11 But stretch out your hand and touch all that he has, and he will curse you to your face.” 12 And the Lord said to Satan, “Behold, all that he has is in your hand. Only against him do not stretch out your hand.” So Satan went out from the presence of the Lord.
Check out this article by Vincent Cheung:
http://www.vincentcheung.com/2005/05/31/the-author-of-sin/
Cheung's answer to the charge that Calvinist theology makes God the author of sin is, "so"?