There are two clear possibilities. One is that it was at that time that they began to use the name of the Lord, which in Hebrew is Yahweh (יְהוָֽה); the other is that they began to pray to and trust in the one true God. The latter is what is meant, but let us discuss the former suggestion. The Pentateuch narrative leaves open the possibility in Exodus 3, which many think is the case, that the name of God was not introduced to the Hebrews until the time of the Exodus. This verse seems to suggest it: “And Moses said unto God, Behold, when I come unto the children of Israel, and shall say unto them, The God of your fathers hath sent me unto you; and they shall say to me, What is his name? what shall I say unto them?” (Ex 3:13) But, as we will discuss when we get to that text, it is entirely possible that the name of God was known to Abraham, Isaac, and Jacob, and that Moses was simply asking which god he was speaking to. In that case, “calling on the name of the Lord” might mean simply learning of his name. So perhaps God gave his name, Yahweh, to the generation of Seth and Enos. But as an exegesis of Gen 4:26, that does not sound quite right to me. The phrase, “call on the name of the Lord,” is used throughout the Bible in a fairly consistent way, to mean to pray (literally to invoke the name of the Lord in prayer), to worship (“Bless the Lord, o my soul!”: Ps. 104:1), to trust and ally oneself with (“And call ye on the name of your gods, and I will call on the name of the Lord”: 1 Kings 18:24). Those who “call on the name of the Lord” are the faithful followers of God. If, as I think is fairly clear, that is what the text means here, that seems to imply that it was not until the generation of Enos, or possibly of Seth, that men took the notion of worshiping God seriously. This says something quite damning about Adam and Eve: apparently, they did not learn from their treatment at the hands of God to call upon the name of the Lord. But what about Abel? You might say that this does dishonor to the memory of the righteous Abel, but since he was killed, he was not made “the father” of the herdsmen, either; that honor is given to Jabal. In the same way, Seth, or perhaps Enos, is made the first man to introduce the worship of the Lord, i.e., to introduce the practice among men.