Ok... I took so long getting back here, sorry! Here are my original five assertions, with quotes as to why I asserted them. (But I once again make the disclaimer - my interpretation of these quotes is my own, and my opinions are my own...)
Going back over my original list, I thought it would be good to add quotes for each assertion. So here goes:
1. Baha'i understanding of sin stands on the shoulders of prior manifestations. In most cases, there are not "definitions" of sin - there is an assumption that everyone already knows what we are talking about. I think this is significant, given Baha'u'llah's role in reconciling the various religions.
And among the teachings of Bahá'u'lláh is that religion is a mighty bulwark. If the edifice of religion shakes and totters, commotion and chaos will ensue and the order of things will be utterly upset, for in the world of mankind there are two safeguards that protect man from wrongdoing. One is the law which punishes the criminal; but the law prevents only the manifest crime and not the concealed sin; whereas the ideal safeguard, namely, the religion of God, prevents both the manifest and the concealed crime, trains man, educates morals, compels the adoption of virtues and is the all-inclusive power which guarantees the felicity of the world of mankind. But by religion is meant that which is ascertained by investigation and not that which is based on mere imitation, the foundation of divine religions and not human imitations.
(Abdu'l-Baha, Foundations of World Unity, p. 30)
532. Not only must irreligion and its monstrous offspring, the triple curse that oppresses the soul of mankind in this day, be held responsible for the ills which are so tragically besetting it, but other evils and vices, which are, for the most part, the direct consequences of the "weakening of the pillars of religion," must also be regarded as contributory factors to the manifold guilt of which individuals and nations stand convicted. The signs of moral downfall, consequent to the dethronement of religion and the enthronement of these usurping idols, are too numerous and too patent for even a superficial observer of the state of present-day society to fail to notice. The spread of lawlessness, of drunkenness, of gambling, and of crime; the inordinate love of pleasure, of riches, and other earthly vanities; the laxity in morals, revealing itself in the irresponsible attitude towards marriage, in the weakening of parental control, in the rising tide of divorce, in the deterioration in the standard of literature and of the press, and in the advocacy of theories that are the very negation of purity, of morality and chastity -- these evidences of moral decadence, invading both the East and the West, permeating every stratum of society, and instilling their poison in its members of both sexes, young and old alike, blacken still further the scroll upon which are inscribed the manifold transgressions of an unrepentant humanity.
(Compilations, The Compilation of Compilations vol. I, p. 237)
2. Baha'i understanding of sin is (as stated) "going against God's will"
Say: Commit not, O people, that which will bring shame upon you or dishonor the Cause of God in the eyes of men, and be not of the mischief-makers. Approach not the things which your minds condemn. Eschew all manner of wickedness, for such things are forbidden unto you in the Book which none touch except such as God hath cleansed from every taint of guilt, and numbered among the purified.
(Baha'u'llah, Gleanings from the Writings of Baha'u'llah, p. 277)
3. Baha'i understanding of sin is subservience to our physical natures. My understanding here is that we have physical natures that are required to move us forward in THIS life, but when we live attached to these physical natures, we are in sin. (Reference to Buddhist detachment, in my opinion)
This physical world of man is subject to the power of the lusts, and sin is the consequence of this power of the lusts, for it is not subject to the laws of justice and holiness. The body of man is a captive of nature; it will act in accordance with whatever nature orders. It is, therefore, certain that sins such as anger, jealousy, dispute, covetousness, avarice, ignorance, prejudice, hatred, pride and tyranny exist in the physical world. All these brutal qualities exist in the nature of man. A man who has not had a spiritual education is a brute. Like the savages of Africa, whose actions, habits and morals are purely sensual, they act according to the demands of nature to such a degree that they rend and eat one another. Thus it is evident that the physical world of man is a world of sin. In this physical world man is not distinguished from the animal.
All sin comes from the demands of nature, and these demands, which arise from the physical qualities, are not sins with respect to the animals, while for man they are sin. The animal is the source of imperfections, such as anger, sensuality, jealousy, avarice, cruelty, pride: all these defects are found in animals but do not constitute sins. But in man they are sins.
(Abdu'l-Baha, Some Answered Questions)
4. The worst sin that is pardonable is backbiting - this supports the thrust of this dispensation toward unity. To think charitably of others, even to the point of avoiding any kind of backbiting is the call of the day.
If ye become aware of a sin committed by another, conceal it, that God may conceal your own sin. He, verily, is the Concealer, the Lord of grace abounding. O ye rich ones on earth! If ye encounter one who is poor, treat him not disdainfully. Reflect upon that whereof ye were created. Every one of you was created of a sorry germ. It behoveth you to observe truthfulness, whereby your temples shall be adorned, your names uplifted, your stations exalted amidst men, and a mighty recompense assured for you before God.
(Baha'u'llah, The Summons of the Lord of Hosts)
"As regards backbiting, i.e. discussing the faults of others in their absence, the teachings are very emphatic. In a Tablet to an American friend the Master wrote: 'The worst human quality and the most great sin is backbiting, more especially when it emanates from the tongues of the believers of God. If some means were devised so that the doors of backbiting were shut eternally and each one of the believers unsealed his lips in praise of others, then the Teachings of His Holiness Bahá'u'lláh would spread, the hearts be illumined, the spirits glorified, and the human world would attain to everlasting felicity.' (Quoted in Star of West, Vol. IV. p. 192) Bahá'u'lláh says in Hidden Words; 'Breathe not the sins of others so long as thou art a sinner. Shouldst thou transgress this command ACCURSED ARE THOU.' The condemnation of backbiting could hardly be couched in stronger language than in these passages, and it is obviously one of the foremost obligations for Bahá'ís to set their faces against this practice. Even if what is said against another person be true, the mentioning of his faults to others still comes under the category of backbiting, and is forbidden."
(Compilations, Lights of Guidance, p. 88)
5. The UNPARDONABLE sin is failure to educate children. In context I think this means keeping a child back from education, but it can be interpretted far more broadly than that. This particular sin supports the great Baha'i philosophy that religion is the great educator of humanity, and that God has done us the greatest good by perpetuating revelation to us. It also supports the Baha'i idea that sin ultimately is the result of ignorance.
484. Failure to Educate Child is an Unpardonable Sin
"This is a sin unpardonable, for they have made that poor babe a wanderer in the Sahara of ignorance, unfortunate and tormented: to remain during a lifetime a captive of ignorance and pride, negligent and without discernment. Verily, if that babe depart from this world at the age of infancy, it is sweeter and better. In this sense, death is better than life; deprivation than salvation; non-existence lovelier than existence; the grave better than the palace; the narrow, dingy tomb better than the spacious, regal home; for in the sight of mankind that child is abased and degraded and in the sight of God weak and defective. In gatherings it is ashamed and humiliated and in the arena of examination subdued and defeated by young and old. What a mistake is this! What an everlasting humiliation!"
(Compilations, Lights of Guidance, p. 145)