He wants to paint a picture that his party or NDA will have a strong military, but he (and his audience) doesn't have a clue as to what that really means. Neither he nor the listeners know anything about increasing force mechanization, or improving night fighting capability, or modernizing the artillery, or reorganizing the corps structures - those issues, the real issues that need to be addressed are way beyond their comprehension or knowledge. So propose the only solution that he and his listeners know - double the size. Populist sloganeering which, if actually implemented, will only lead to lessened combat capability, because all the increased manpower will be left without adequate tank, IFV, arty and air support - these cannot keep up with our present needs. So we will have a million armymen unsupported by all the stuff mentioned above, which means that instead of being a bigger force that can project more power, they will become a bigger target for the enemy, and sitting ducks for smaller, more modernized units.
The need of the hour is modernization, not increasing the already bloated size. But then these plans are made by the army, and not by politicians, and BJP politicians, like those of any other party, will simply mouth off what the listeners want to hear. Ask Rajnath singh about what measures he would take to improve the night fighting capability of our frontline infantry or armor units, and he would probably not understand a word of the question. But he has to keep up the pretense that his party is "tough" and "militaristic", so he has to offer these simplistic promises which, if actually implemented, would be disastrous for the country.
This is why politicians should formulate the military's objectives and intended capabilities, while how to achieve those capabilities and objectives should be planned by the forces themselves.