Sforno on Genesis 4:26/ספורנו על בראשית ד׳:כ״ו

1אז הוחל לקרא בשם ה, at that time the righteous people of the earth began to preach monotheism to the public. The meaning is similar to Genesis 21,33 ויקרא שם בשם ה' א-ל עולם, “Avraham proclaimed there the name of the Lord, the Lord of the universe.” The time had come to publicly confront and refute the arguments of the idolaters in that period.