To sin is to do something contrary to the will of the Lord. It is to be willfully disobedient. Transgression, on the other hand, is the violation of a law or rule that may or may not be against the will of the Lord. Thus, all sins are transgressions but not all transgressions are sins.
Sin is breaking a law with knowledge that a law is being broken. Adam didn’t have knowledge of good and evil before partaking of the forbidden fruit, so his act was a transgression of the law, not a sin against the law.
The Bible clearly notes a difference between sin and transgression
– Psalms 25:7 -> “Remember not the sins of my youth, nor my transgressions: according to thy mercy remember thou me for thy goodness’ sake, O Lord.”
– Joshua 24:19 -> “And Joshua said unto the people, Ye cannot serve the Lord: for he is an holy God; he is a jealous God; he will not forgive your transgressions nor your sins.”
The first mention of sin in the Bible is in regards to Cain.
Genesis 4:6-7 -> “And the Lord said unto Cain, Why art thou wroth? and why is thy countenance fallen? If thou doest well, shalt thou not be accepted? and if thou doest not well, sin lieth at the door. And unto thee shall be his desire, and thou shalt rule over him.”
Adam and Eve’s partaking of the forbidden fruit is referred to as transgression.
Romans 5:14 -> “Nevertheless death reigned from Adam to Moses, even over them that had not sinned after the similitude of Adam’s transgression, who is the figure of him that was to come.”