'Reuben my firstborn' means faith which seemingly occupies the first place. 'You are my might' means that through that faith comes the power which good possesses. 'And the beginning of my strength' means that through that faith comes the initial power which truth possesses. 'Excelling in eminence and excelling in worth' means the resulting glory and powerfulness. 'Light as water' means that faith alone does not possess such qualities. 'May you not excel' means that neither does it have any glory or powerfulness. 'Because you went up to your father's bed' means because when separated from the good of charity faith is involved in a foul liaison. 'At that time you profaned [it]' means that if it were joined to evil, profanity would exist. 'He went up to my couch' means because it would contaminate spiritual good in the natural.