John Calvin Commentary Genesis 4:24

"If Cain shall be avenged sevenfold, Truly Lamech seventy and sevenfold." — Genesis 4:24 (ASV)

Cain shall be avenged sevenfold. It is not my intention to relate the ravings or the dreams of every writer, nor should the reader expect this from me. Here and there I allude to them, though sparingly, especially if there is any appearance of deception, so that readers, being often admonished, may learn to take heed.

Therefore, with respect to this passage, which has been distorted in various ways, I will not record what one or another may have said, but will content myself with a true exposition of it. God had intended that Cain should be a horrible example to warn others against committing murder, and for this purpose had marked him with a shameful stigma. Yet, so that no one would imitate his crime, He declared that whoever killed him would be punished with sevenfold severity.

Lamech, impiously perverting this divine declaration, mocks its severity. For he therefore takes greater license to sin, as if God had granted some singular privilege to murderers. Not that he seriously thinks so; but, lacking all sense of piety, he promises himself impunity and, in the meantime, jestingly uses the name of God as an excuse: just as Dionysus did, who boasted that the gods favor sacrilegious persons in order to obliterate the infamy he had contracted.

Moreover, as the number seven in Scripture designates a multitude, sevenfold is understood as a very great increase. Such is the meaning of the declaration of Christ:

‘I do not say that thou shalt remit the offense seven times,
but seventy times seven’ (Matthew 18:22).