To answer this question, let me humbly remind Sri Ramakrishna and Sarada Devi were no ordinary human beings.Their holy lives and activities make it clear that they descended to earth to save Dharma and show us the right paths.
This becomes clear when Sri Sarada Devi at the age of two indicated that She will marry Sri Ramakrishna.
After the completion of a kirtana, a village-woman who was holding Sarada on her lap, asked Her: Whom would you marry, my daughter? Sarada raised Her Hands and pointed towards Sri Ramakrishna.
Let us now see some of the incidents of Their lives starting from Their marriage to make our idea clearer.
Sri Ramakrishna became immersed in spiritual practices and became God-intoxicated in His teens. On His mother's order, He came to Kamarpukur at the age of twenty-four. Her mother and elder brother were eager to get Him married, but failed to get a suitable bride.
Knowing this, Sri Ramakrishna asked them to go to Jayrambati where Sarada, the daughter of Sri Ramachandra Mukhopadhyay has been providentially reserved for Him ('kuto-bnadha' in bengali) had been staying. Sarada was only five years old at that time.
Sri Ramakrishna went joyfully to marry. On the very first night they were together after marriage
He told Sarada: You see, I can not tolerate the smell of the coconut oil.(Bengali girls used coconut oil for their hair-care at that time). Please place a mat on the floor and I shall sleep there. Sarada immediately came down Herself and slept on the mat.
Sri Ramakrishna returned to Dakshineswar and again dived deep into His sadhana. Sarada had been staying with Her parents. When She was thirteen (May, 1867), Sri Ramakrishna came to Kamarpulkur with His Tantra-Guru (Bhairavi Yogeswari) and summoned Her immediately.
Sri Ramakrishna on the one side held His ideal shining with the spirit of renunciation in front of Her, and started Her training all the worldly duties in detail on the other. He taught Her ideal acts and behaviour in each and every aspect of life. Sarada started feeling 'a ghata filled with bliss' had been established in Her heart.
Staying few months at Kamarpukur, Sri Ramakrishna returned to Dakshineswar and again forgot the world in love of God. She came to Dakshineswar with His father after four years.She was eighteen now. She had to walk sixty miles to reach Dakshineswar. She fell sick on the way and was very anxious as covering such a distance would be impossible with ill heallth .
Mother Kali taking form of of a girl appeared in front of Her and told Her: Do not worry. You will be alright very soon. I have kept Him confined at Dakshineswar for you.
Sarada Devi safely arrived at Dakshineswar and Sri Ramakrishna welcomed Her heartily. Now She stayed for few months with Sri Ramakrishna in the same room.
Sri Ramakrishna asked Her one day : Have you come to make me walk on the wordly path? Sarada Devi replied :Absolutely not. I have come to help you to reach your desired goal. Another day Sarada asked Her: Who am I to you? Sri Ramakrishna replied : A form of My blissful Divine Mother.
After few days, Sarada Devi was worshipped by Sri Ramakrishna as The Mother Goddess on the night of 5 June 1872 (Phalahaarini Kali-Puja). Sri Ramakrishna offered His sadhana and His japamala at Her feet.
He often used to sing a song : I have come to the world with a responsibiliy. Then He used to tell Sarada: Is it mine alone? No. It is yours as well.
Sarada Devi started serving His husband and His devotees maintaining an unthinkabke austere life.
In later years, Sri Ramakrishna told His devotees:
"A Paramahansa has to pass through all stages of life to reach the peak". "Marriage is one of the Ten sanskaras of human life and so it was necessary"."Every act of mine is to set some ideal. I do not like anything except God.It is His will".
When He was asked why He did not have any physical relation with Her wife in spite of this being the Law of God? Sri Ramakrishna replied : Its His will. Do you think He creates all justto lead life like animals?
Sri Ramakrishna gave up His body in 1886. But He remained alive in form of Sarada Devi. He had earlier told His devotees: "She (Sarada) is not an ordinary woman.She is my Shakti"."She is Mother Saraswati Herself, descended to give jnana to all". He had been keeping constant communications with Her till Her Mahasamdhi . She had been the Support of all the disciples and devotees of Sri Ramakrishna.It is She whose instructions were blindly obeyed by all the monk disciples of Sri Ramakrishna. The History shows that without Her, the Ramakrishna Movement would have drowned in Ganges very soon after Sri Ramakrishna's Mahasamadhi.
So the intention of their married life was something totally beyond imagination of the normal individuals like me.Our scriptures say :Achintya khalu ye bhaavaa maa taan tarkena yojayet" :( Do not apply logic in discussing topics beyond perception)
Reference: 1. Sri Sri Ramakrishna-Leelaprasanga, Swami Saradananda, Udbodhan, vol 1 & 2. 2.Sri Sri Ramakrishna -Kathamrita,Sri M, Udbodhan 3. Sri Ramakrishna Bivashita Maa Sarada, Swami Budhananda,.Udbodhan