The trine houses (1st, 5th and 9th) are known as Lakshmi sthana (meaning places of lakshmi). The Goddess Lakshmi is one of the important Divine figures in Hinduism and She signifies wealth, prosperity and all kind of riches and comforts.
The classic text Brihat Parasara Hora Shastra gives the trine (trikone) houses prime importance in matter of wealth in the chapter named “Dhana Yogas”. Where first some verses are about 5-11 axis which have exceptional potentials to give wealth. See here for more
The later verses are on trine lords and trine houses, which are also the potential wealth givers. See the verse from Parasara Hora below.
Brihat Parasara Hora Shastra
“The 9th lord and the 5th lord both are capable of giving wealth. The planet who have the conjunction of these two will also be the bestower of wealth in their Dasa periods, there can be no doubt about it.”
Parasara also signifies the importance of 5th and 9th lord in a verse from Raja yogas sections of his work. We know that the Lagna lord (1st lord) is considered the most important planet for the Birth chart, same as the king or prime minister among all other planets. In the same ways Parasara recognises 9th lord as a minister and 5th lord as a chief minister.
Brihat Parasara Hora Shastra
“The 9th lord is akin to a minister and 5th lord akin to the chief minister. If both have the mutual aspect, the native is entitled to be a king. If they are in conjunction any where or if they are in the 7th house form each other, then the native born in a royal family will certainly be a King.”
The Trine Houses and their lords plays a significant role in formation of so many Raja Yogas and Dhana Yogas by their placement, conjunction, mutual aspect or the exchange of signs.
More about trine lords in articles below.
Parasari Raja Yogas
The most worthy Dhana Yogas
Extreme wealth