If a soul shall sin through ignorance. - Leviticus 4:2
Sin is something more than that of which our conscience convicts us. Our conscience may excuse or palliate our sins, or may fail to detect them for want of proper enlightenment, or may be misled by the practices and sentiments of those around. Therefore we may do things which are grievously wrong in God's sight without realizing their evil or bemoaning it.
All such sin must be met and atoned for ere God can admit us into His holy presence. Sin must be dealt with and put away, not only as it appears to us, but as it is in itself and in the sight of the All-Holy. So, in the types of Leviticus, provision was made for sins of ignorance; and the blood of Jesus cleanseth from all sin, whether known to us or not.
There is more sin in us than any of us know. If we think we have passed a day without conscious sin, we have only to wait till an intenser light is flashed on our motives and intentions - for firelight to be exchanged for electric light - and we shall see specks and flaws. If we do not actually violate known commands, there may be a grievous coming short of the infinite standard of the Divine perfection. Who shall dare to say that be has loved God with all his heart, and soul, and strength? Besides, there is always the liability to sinfulness; and this needs to be perpetually met and atoned for.
It is very needful, then, for us to be perpetually cleansed in the precious blood of Christ. We must ask to be forgiven for the many sins which we know not, as well as for those we know. The work of confession and forgiveness must therefore go on to life's end, applied to each heart and conscience by the Holy Spirit.