He made touching a term for lawful marriage, because it is a metaphor for it, as His saying: "before you touch them" or "when you have touched women". And adultery is not like that; it is only said of it: he committed fornication with her and he acted wickedly with her, and similar expressions. It is not appropriate to consider metaphors and manners in it. The term 'bigha' refers to the immoral woman who seeks men. It is a form of 'fa'ool' according to Al-Mubarrad, 'bighwi', as the waw is assimilated into the ya. Ibn Jinni said in his book Al-Tamam: it is a form of 'fa'il', and if it were a form of 'fa'ool', it would have been said 'bighu' as it is said: such-and-such is 'nahu' from wrongdoing. And let us make it a sign, the reason for which is omitted, meaning: and let us make it a sign for the people; we did that. Or it is connected to an implied reason, meaning: to clarify our power by it and to make it a sign. An example of this is: "And Allah created the heavens and the earth in truth and so that every soul may be recompensed for what it earned" and His saying: "And thus We established Yusuf in the land and to teach him." The decree is predetermined, inscribed in the tablet; you must follow it. Or it was a matter truly deserving to be and to be decreed because it is a sign and a mercy. The intended meaning of the sign is: the lesson and the proof of Allah's power, and of mercy: the laws and kindnesses, and what was a cause for the strength of faith and the means to obedience and good deeds. It is worthy of creation.