The oil filter on your car operates by running the oil in your car through the filter in order to filter out any harmful or damaging particles. However if the filter becomes clogged with lots of junk it will eventually struggle to provide oil for the car, starving it of oil and possibly causing engine damage. To avoid this there is a bypass valve that activates when the filter is clogged, when this happens all oil is bypassed past the filter and goes straight back into the engine, unfiltered, allowing possible harmful particles to go into the engine damaging or reducing the effectiveness of its performance.
The Christian life is exactly the same, we are called in 1 John 4 to test the spirits to see whether they come from God. When we fill our minds and hearts with lots of worldly /ungodly stuff like movies, shows, secular music, books, etc our filter becomes clogged, eventually its so full it looses its ability to filter it at all and all the harmful stuff goes straight into our lives without filtering, causing damage to our lives, minds, and spiritual walk. If it goes too long, irreparable damage can occur decreasing our spiritual performance and abilities. Getting more into the bible is only one part of the solution, we must first stop the source of bad influx into our minds/ heart and then begin to clean our filter through Gods word and renew our minds as it says in Romans 12:2.