Dear BelieveItOarKnot,
I only only partially agree with some of what you stated. I'll try to explain below.
Mankind commits sins because mankind was created spiritual marred and subject to vanity. This spiritual flaw gives mankind a carnal mind. The carnal mind will put the needs of "self" over loving others and loving God. We show our love for God by our obedience to Him. But since the carnal mind puts the needs of self first, mankind will frequently disobey God. When a person disobeys God, they are sinning.
Satan was created to be mankind's tempter and destroyer. He is not the source of mankind's sin. Satan merely tempts us to sin. From his temptations, mankind will sin more frequently.
When Christ came in the flesh, He had the Spirit without measure. Because He did, Christ never developed a carnal mind. And since Christ never developed a carnal mind, He ALWAYS obeyed His Father over His own needs. As a result, Christ never sinned.
As for why sins are not counted against a faithful believer, it is only become they are covered by the blood sacrifice of Christ. If a person is not covered by the blood of Christ, they will be held to account for their sins.
Your comment on "two parties, man and tempter, walking in the same pair of shoes" is somewhat true.
Here is how it happens:
From the beginning, Satan has been mankind tempter from "without". However, this changed with Judas. With Judas, Satan entered into Judas (via the spirit of anti-Christ) and tempted Judas to sin from "within". When this happened to Judas, he already had a small measure of the Holy Spirit within Him. Now with the spirit of anti-Christ indwelling Judas, too, there were "two" in the "same pair of shoes".
Judas is a "type" for an apostate believer. After Paul's death, all the babes in the churches that were started were indwelt with the spirit of anti-Christ. When this happens to a babe, they will be like Judas, having both the small measure of the Spirit and the spirit of anti-Christ within them. And like Judas, the babe will betray Christ and become unfaithful. The babe becomes unfaithful because they have spiritually fornicated with Satan. In other words, the babe started following the ways of Satan instead of the ways of Christ.
Note: When the spirit of anti-Christ enters a babe, the Abomination of Desolation occurs within the babe (God's Temple).
After a babe becomes a "man of sin" (like Judas), they will fall from grace.
Since the death of Paul, all babes have experienced Satan's deceptions and have fallen from grace. No new believer can avoid it happening to them.
These two scriptures below teach why it happens:
Isa 28:9 Whom shall he teach knowledge? and whom shall he make to understand doctrine? Them that are weaned from the milk, and drawn from the breasts (converted believers). 10 For precept must be upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little: 11 For with stammering lips and another language (spiritual language) will he speak to this people. 12 But the word of the LORD was unto them (babes who draw milk) precept upon precept, precept upon precept; line upon line, line upon line; here a little, and there a little; that they might go, and fall backward, and be broken, and snared, and taken (by Satan).
Mat 12:43 When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest, and findeth none. 44 Then he saith, I will return into my house from whence I came out; and when he is come, he findeth it empty, swept, and garnished. 45 Then goeth he, and taketh with himself SEVEN other spirits more wicked than himself, and they enter in and dwell there: and the last state of that man is worse than the first. Even so shall it be also unto this wicked generation.
The spiritual symbol of an unclean spirit represents a spirit which teaches Satan's false truth through lies and deceptions.
Since a new believer remains spiritually blind (Mark 8:21-25) after receiving the Early Rain of the Spirit, they cannot replace their worldly false beliefs with the truth of Christ. ONE unclean spirit leaves but comes back with SEVEN more. The number "seven" represents perfection. In this case, the number seven represents the perfection of Satan's lies/deceptions which come to a believer by the indwelling of the spirit of anti-Christ. Now, instead of ONE unclean spirit within the believer, they now have EIGHT. The number eight is a spiritual symbol which represents a new spiritual condition. In this case, the new spiritual condition is worse than the first.
This "worse than the first" spiritual condition causes the believer to become a False Prophet, a Man of Sin, a Minister of Satan and a Seven Headed Beast with Ten Horns & Crowns.
For the apostate babes who are Elect, Christ will come to them a second time (His second coming) and pour out the Latter Rain. The Latter Rain will restore the babe and give them a new birth as a child of God. Judgment will then immediately follow to remove and destroy the spiritual things (the chaff) from within them that has caused them to be carnally mind and sinful. Those spiritual things are the spirit of anti-Christ and the person's marred and carnal spirit.
The verses below describe this judgment:
Mat 24:37 But as the days of Noe were, so shall also the coming of the Son of man be. 38 For as in the days that were before the flood they were eating and drinking, marrying and giving in marriage, until the day that Noe entered into the ark, 39 And knew not until the flood came, and took them all away; so shall also the coming of the Son of man be. 40 Then shall two be in the field (within one babe); the one shall be taken (spirit of anti-Christ), and the other left (Holy Spirit). 41 Two women shall be grinding at the mill (within one babe); the one shall be taken (marred and carnal spirit), and the other left (new divine spirit).
For the apostate babes are not Elect, Christ will not return to them and convert them. As a result, they will die in their sins and will receive their portion (salvation) with the unbelievers in the Lake of Fire.
The babes will suffer "loss" but they will still be saved:
1Cor 3:13 Every man's work shall be made manifest: for the day shall declare it, because it shall be revealed by fire; and the fire shall try every man's work of what sort it is. 14 If any man's work abide which he hath built thereupon, he shall receive a reward. 15 If any man's work shall be burned, he shall suffer loss: but he himself shall be saved; yet so as by fire.
Joe