These three levels of relationship between husband and wife reflect the three general levels of relationship between G-d and man.
A tzadik (a consummately righteous person) is someone who is so completely devoted to G-d that he never regards himself as a separate entity or individual. True, his observance of Torah and the commandments is suffused with his intention to cling to and become one with G-d by fulfilling His will, and he experiences Divinity with love and fear. Yet he attributes it all to G-d's infinite grace and providence. As our sages say (Avot 3:7): "Give [i.e., attribute] to Him that which is His, for you and all that is yours are His."
G-d responds by proudly attributing all the good in reality to the merit of the tzadik. In fact, as mentioned above, His motive in creating the world was the pleasure He would derive from the good deeds of the righteous.
The second level of relationship corresponds to the consciousness of the beinoni ("intermediate" servant of G-d).
In all modes of behavior–thought, speech, and action–the beinoni has renounced the lifestyle bred by the unrectified imagination and thus is free of sin, but his motives are not yet totally pure; he has not surrendered his selfhood. He is committed to helping G-d bring the world to perfection by fulfilling His will with joy, yet remains aware that he is working for his own good as well.
Our sages interpret the phrase which concludes the verse: "You shall therefore keep the commandments, the rules, and the laws which I command you today to do them" (Deuteronomy 7:11) as implying: "today [in this world] to do them and tomorrow [in the world to come] to receive their reward" (Eiruvin 22a; Avodah Zarah 3a.).
The beinoni takes this to mean that though the challenge of this world ("today") is to perform G-d's commandments faithfully, in return, he will surely inherit ("tomorrow") the reward of the world to come.
A tzadik, on the other hand, understands this teaching to mean that one should "today" be concerned only with "today" and its tasks and have no concern for "tomorrow" and its rewards. For in truth, "one hour of teshuvah ["return" to G-d through self-rectification] and good deeds in this world is greater than all the life of the world to come" (Avot 4:17), for in this world one can unite totally with G-d by performing His will. The tzadik's service of G-d is strictly for its own sake. His unconditional desire to serve and become one with Him precludes any concern with receiving a reward, even that of the world to come.
Rabbi Shneur Zalman of Liadi illustrates this idea as follows (Ma’amarei Admor HaZaken HaKetzarim, p. 461):
The story is told in the Midrash (Shir HaShirim Rabbah 1:31.) of a Jewish woman who was married for many years, but had not had children. Her husband decided therefore to divorce her, so he went to Rabbi Shimon bar Yochai, of blessed memory, who told him that just as they celebrated their marriage with joy, so should they celebrate its severance with joy.
The husband prepared a great feast, at the height of which he asked wife to choose whatever of his possessions she desired, assuring her that he would not refuse her anything.
And what did she do? She served him so much wine that he got drunk and went to sleep, and then told her servants to take him on his bed into her bedroom.
The following morning, when he awoke and found himself in her home, he asked her why he had been brought there–wasn't it clear that he intended to divorce her? She replied: "Didn't you tell me that I could take whatever I wanted? Well, I desire neither gold, nor silver, nor precious gems, nor pearls; all I want is you. You yourself are the sole object of my desire."
When the husband heard this, he again became enamored of his wife, and took her back. And in this merit, the Holy One, blessed be He, granted them children.
So it is with regard to the service of G-d. As it is stated (Song of Songs 8:2): "I will serve you aromatic wine, the fragrance of my pomegranates"–this refers to the fact that the least worthy of Israel is as full of [merits accrued by fulfilling G-d's] commandments as a pomegranate is of seeds. [The bride, Israel, serving the groom, G-d, means arousing Him] to descend [and dwell] among us, for [by doing so, we are in effect saying to Him:] "Who have I in heaven, and I desire nothing beside You on earth" (Psalms 73:25). Meaning: I have no desire for any good thing or delight, neither in the higher garden of Eden nor in the lower garden of Eden; I desire nothing but You.
In this merit, one will "bear" spiritual progeny–a son and a daughter, i.e., love and fear of G-d. [Love and fear of G-d are considered spiritual progeny inasmuch as they are the "offspring" of intellectual meditation].
And also on the physical plane, "he will have offspring and [merit] long life" (Isaiah 53:10).