Adam begins differently from every man who followed him because Adam did not have to learn about God from another human being. He knew God personally. He had lived in the garden in His presence, had heard His voice, received commandments from Him, and knew what it was like to live with Him without the separation that came because of the Fall.
Before Adam was cast out of the garden, God clothed him and gave him further instructions. After the Fall, Adam was on the earth for 930 years. He had many sons and daughters and he taught them of his experiences with God. He taught them how to worship him, how to use altars and about the coming Messiah who would save and redeem them from the Fall.
It is hard for us to comprehend what it would have been like to live for 930 years and how much posterity Adam would have had by the time he left this earth. Eve and her daughters would have been having children for many more years than women do today, I would say hundreds of years. So Adam would have spent his life teaching his posterity about his experiences with God and how to know God.
In the family line of the Messiah there are some fathers that we are told about who came to know God and who shared that knowledge with others. God helped me to see the opportunities these men had to share thoir experiences with others, even though it is not recorded.
Adam lived alongside Seth for 800 of Seth’s 912 years, Enosh for 695 of his 905 years, Enoch for 308 of his 365 years, Methuselah for 243 of his 969 years, and Lamech for 56 of his 777 years.
Lamech, Methuselah, Enoch, Enosh and Seth had plenty of time to have opportunity to hear from the mouth of Adam what it was like to live in the presence of God and for Adam to teach them directly how to be faithful and how to worship God, as Adam had done with Abel.
In the 1,600 hundred years between the fall and the flood the number of people who believed in God reduced to those who entered the ark. Obviously those who did believe in God gathered together to strengthen each other.
For the first 243 years that Enoch was walking with God and raising his family Adam was still alive. No doubt he would have met with Adam and they would have rejoiced together, sharing their experiences with God. That also means that both Methuselah and Lamech had the opportunity to be taught about God and how to worship by Adam and Enoch. Both men who had walked with God.
We are not told of the experiences that Methuselah and Lamech had with God, however they lived with Noah during most of the 600 years of his life before the flood and Shem for his first 98 years and would have taught them what they were taught by Adam and Enoch and their own experiences. Noah believed and worshiped God in righteousness so that Noah walked with God like Enoch and Adam. Shem also believed and was righteous all his days.
Shem was alive for the first 110 of Isaac’s 185 years of life and the first 50 of Jacob’s 147 years of life. Therefore Isaac and Jacob not only had the teachings of Abraham but also Shem and both men had come into the presence of God. Shem was still alive when God appeared to Isaac. I presume they must have sought each other out to share in the joy of their experiences. Just as Isaac and Jacob would have done after God appeared to Jacob.
These men not only heard the words of men who had been in the presence of God but also came into the presence of God themselves. So in the first 2,500 years from the fall the knowledge of God was real and men actually experienced the presence of God therefore they knew God. Much different to the preachers of today who debate and argue with each other about the nature and being of God and yet have never met him.
I understand that some of these things are not explicitly said in the bible however with the Holy Spirit as our guide we can know the things. Also some things are self evident. If a man tells me he has children, obviously a woman or women were involved, I do not need to be told that. In the same way, when Abel knows how to worship God acceptably, that tells us about what had been taught in Adam's family.