How early was this sacrificial system known?

Answer

"By faith Abel offered unto God a more excellent sacrifice than Cain, by which he obtained witness that he
was righteous, God testifying of his gifts." Heb. 11: 4. See Gen. 4: 3-5; 8: 20.

Who, therefore, did the speaking through these men?
What is God's love able to do for His children?
How often will they congregate to worship the Lord?
What kind of labor is to be done through the week?
On what day was John in the Spirit?
How does James say the rich have lived?
Would God have His people unite in these combinations?

Questions & Answers are from the book Bible Readings for the Home Circle