Our Mishna on Amud Aleph delineates three methods to accomplish betrothal (Kiddushin): Via an exchange of an object of value, via a written contract, or sexual intercourse. As we have remarked numerous times, the paradigm of marriage is used to explain a person’s relationship with God.
Rav Yaakov Yosef Mipolnoe understands these three methods of accomplishing marriage as also representing three stages of man’s relationship with God. Kesef, which is money, represents desires and aspirations. In Hebrew, "lichsof" means to pine after, as in the famous Yedid Nefesh zemer:
כי זה כמה נכסוף נכסף
For so much has this yearning been
The next stage is contractual and verbal, which is represented by the words in the contract. This is after the initial excitement and honeymoon wear off, and now what holds observance in place is commitment.
And then, the final stage, which is represented by sexual intercourse, involves the union of both aspects together. There is a deep, binding love and wish for attachment, combined with a sense of responsibility and duty.
As in the relationship with God, so too in a healthy relationship, there must be love and responsibility. Marriage cannot be merely fun and games, nor should it be drudgery. Life is at its most fulfilling when we are taking on challenges that are meaningful, difficult, but not overwhelmingly difficult. Relationships also feel best when there is constant work to understand and connect; both out of love and moral obligation.