Answer
Almighty Allah says And give women their Mahr (dowry). (Nisaa verse 4)
To give mehr is the order of Allah. As muslims, we express submission to the orders of Allah and believe that He is Hakim, (The All Wise) Every order of Allah is filled with wisdoms. Our limited understanding may not be able to comprehend all the wisdoms behind an order of Allah. However the Fuqaha (jurists) have stated that the mehr (legally) is in lieu of the private part. A man should honour a woman before having access to her. Mehr is not given for security purposes. The very constitution of Nikah offers security to a woman
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai