One should understand that navamsha is the main chart of marriage, dharma/religion, luck and overall well being also. Navamsa chart is the storage of our prarabdha. It is the expansion of the 9th house.
Now, don’t confuse that marriage is 7th house then why navamsha is taken if it is expansion of the 9th house.
The 9th house is the storage of prarabdha karma, 4th from the 6th house. Marriage is the main prarabdha, or the people with whom we interact are also. It is the 3rd house from 7th, 3rd house shows those things which we cannot avoid, it becomes unconscious. 3rd house from lagna is also 10th house from 6th house of prarabdha.
Actually, marriage is the most important part of our life, it is the shakti or strength of us.
You must have seen, many people are either destroyed or rise in their life after marriage. There is a 180 degree change in life after marriage. It is the 7th house, which holds the strength of the lagna. Now, 7th house is not only marriage, it is also the house of the people with whom we interact. Not a single person on this planet can survive alone. He/she will need someone, some relations.
To be honest, navamsha shows many things about marriage, but D-7 children and prosperity, D-12 compatibility with family and D-30 fortune and misfortune has to be seen for complete analysis of marriage. Marriage is not a small thing. Life revolves around it, those who are not married, then partners & people play an important role.
Therefore, navamsha becomes the chart from which we can access the prarabdha or say bhagya/fate.
So, everyone should analyse navamsa. It is a myth that it activates after 36 and becomes the main chart.