There is a general feeling when it comes to God (not religion) that we work or relate or interact with God only when we feel like it (in a spontaneous sense). When we don't "feel" the love from God, we do not really worry about God. But actually our Acharyas teach that we have to "force" certain issues. Krishna asks Arjuna to "control" his mind through practice and detachment. Practice means we have to force our mind to behave in a certain way.
Spiritual inertia is a natural element of material culture. Our culture is advancing in the name of technology to increased levels of inertia or simply put laziness. Think about it - inventions such as automobiles, tractors, cell phones, computers make things efficient, quick and orderly but creates a mentality that machines will do the work and I just need to control the machine. Science is advancing more and more towards increasing technology however it is also drastically promoting laziness. When was the last time you wrote a letter by hand and mailed it to your loved one? So this is the situation - this inertia has largely impacted our spiritual life as well.
We fear change, and lack the drive to beat the blues in terms of spiritual inertia or laziness. But if we want to progress towards Krishna, then no machine or sporadic spontaneous feelings of God will cut it. We have to approach this "military" style meaning with intent and conviction. We have to force our enthusiasm to be in Krishna consciousness.
The more we show our conviction towards Krishna in terms of disciplining our mind (forcefully) then surely Krishna will reciprocate and when that reciprocation happens, we know He exists and there is no greater feeling than knowing that Krishna exists and He is looking out for us. This experience or realization will cultivate within us a spontaneous attachment towards Krishna.
So yes purity is the force, so lets force it!