“and bring happiness to his wife.” The wife would be happy to have her new husband with her at home, but beyond that, there is a good chance that in that year she would become pregnant, and it was a blessing to the woman and to the whole family for her to have a baby.
We must keep in mind that in the biblical culture most people lived in clans and in very close proximity to their relatives. Also, it was the custom that a woman left her family and joined the clan of her husband’s family. Genesis 2:24 says a man leaves his father and mother and is joined to his wife, but that is not what happened in the physical world, it was the woman who left her family and joined the husband’s family and clan. Since it was typical for a girl to be married around 12-14 years of age, we can see that it would be very unsettling and even scary for a girl of 12-14 years of age to be pulled from her family and taken to live in another clan that might be some day travel from her own clan. Furthermore, there was no easy communication in those days, and especially for women it was not common for them to travel outside the village where they lived. That meant that for a young wife to see any familiar family member could be rare or even basically never, and even more so once she started having children which would certainly restrict any travel she might have once been able to do. So in order to allow the young wife to become acclimatized to her new social environment the Law of Moses provided for the husband to stay home with her the year after they were married and thus provide some stability, protection, and love for her. During that first year the man would have his regular job, but he would not be away from the house engaged in war or doing things involved with public duty.