Hebrew parents would dedicate their first child to God. The words "beginning" and "first-fruit" means that Reuben belonged to God in a special way. Alternate translation: "the first-fruit of my manhood."
Jacob compares Reuben to water in a strong current to emphasize that he cannot control his anger and he is not stable. (See: [[rc://en/ta/man/translate/figs-simile]])
## because you went up to your father’s bed. Then you defiled it; you went up to my couch. ##
This refers to when Reuben slept with Bilhah in [Genesis 35:21](../35/21.md). This can be made explicit: "because you went to my bed and had sex with Bilhah my concubine. You brought shame on me." (See: [[rc://en/ta/man/translate/figs-euphemism]] and [[rc://en/ta/man/translate/figs-explicit]])