how to reconcile the statement that the only definition of sin is trangression with the idea that sin is nature also?

 The sources you provided consistently define sin as the "transgression of the law". This is presented as the "only definition of sin given in the word of God".

However, the sources reconcile this with the idea of a "sinful nature" by explaining that this nature is a result of previous transgression and the source from which further transgressions spring.

Here's how these concepts are interconnected:

• The Origin of Sinful Nature through Transgression: Man was originally created perfect, "in the image of God," with pure thoughts and holy aims, and in harmony with God's law. However, through disobedience (transgression), his powers were perverted, and selfishness took the place of love, weakening his nature. The "fall of man" resulted from Adam and Eve's single act of disobeying God's express command regarding the forbidden fruit. This act, though seemingly small, was a "transgression of God's immutable and holy law" and "opened the flood-gates of woe upon our world".

• Sinful Nature as "Carnal Mind" at Enmity with God's Law: The sources frequently refer to the "carnal mind" or "natural inclinations" which are described as "enmity against God; for it is not subject to the law of God, neither indeed can be". This perverted nature is a consequence of the original sin, making it difficult for humans to obey God's law. Therefore, the existence of a "sinful nature" is not an alternative definition of sin, but rather the state of humanity subsequent to the act of transgression, which continues to lead to further transgression.

• Transgression as the "Outworking" of the Sinful Nature: Sin, defined as transgression, is also described as "the outworking of a principle at war with the great law of love". This "principle at war" is the sinful nature. So, while the underlying sinful nature (e.g., covetousness, lust, anger, selfishness, pride) is inherent due to the Fall, it manifests itself as sin when these inclinations lead to concrete "departures from God's expressed will". For instance, "indulging anger, lust, covetousness, hatred, selfishness, or any other sin, we become servants of sin". Even "evil thoughts" or "unholy imaginations" are considered a part of this transgression.

• Violation of Natural Law is Transgression of God's Law: The sources extend the concept of God's law beyond the Ten Commandments to include "natural laws" governing our physical being. "It is as truly a sin to violate the laws of our being as it is to break the ten commandments. To do either is to break God's laws". This includes "indulgence of perverted appetite," "health-destroying, brain-enervating habits," and "excessive indulgence in eating, drinking, sleeping, or seeing". Such actions weaken the physical, mental, and moral powers, dishonoring God. Ignorance of these laws is no excuse for transgression.

• The Law as the Detector of Sin: Crucially, the sources emphasize that the law is the standard or "mirror" by which sin is known and detected. Without the law, there would be no knowledge of sin, and transgression would not exist. This reinforces that sin is fundamentally an act against the established divine order.

In essence, the "sinful nature" is the corrupted state of humanity resulting from Adam's initial transgression of God's law. This corrupted nature then expresses itself through further transgressions (actions, thoughts, intentions, and even violations of physical well-being), all of which are defined as sin because they deviate from God's holy and perfect law. Therefore, the two ideas are not contradictory but represent the cause and effect, or the internal inclination and its outward manifestation, all viewed through the lens of God's unchanging law.