4th house is all about mother, happiness, peace of mind, comfort, homeland people, domestic environment, vehicles, luxury, farm, education, building etc…
So the success of the 7th house makes the 4th house things happy ..let’s explore…
When you get to marry the right partner, your mother is the first person who will become happy followed by your relatives
When you get a promotion in your work (7th house is 10th from 10th too), your mother becomes happy/expanding of inner peace too/increase the luxury
When you start a business partnership, that will give a boost to the happiness of your mother and subsequently to your comfort zone and luxury
You become a celebrity/status/mass fame in public (7th house) that’s also the happiness factor for your family people
When you learn to interact with every other person (7th house) in the world …that’s also the happiness of your primary education (4th house)