Supplementing your diet.
Vitamins and supplements are good, right? They can be, but can you imagine supplementing your entire diet with vitamins. Like not eating any food, but only taking vitamins. That would be super unhealthy, right?! Of course, vitamins are good, but we need food.
Well, what about our spiritual diet? Reading devotions, commentaries, listening to Christian podcasts, etc. are all good, right? But what if you're substituting all of these instead of having time in the pure word of God? That's also unhealthy. Sure, all those things are good and can add to our Christian walk, but we need the Bible. The pure, unadulterated word of God.
In Deuteronomy 8:3 it is written, (and then 34 reiterated by Jesus) that man shall not live by bread alone; but man lives by every word that proceeds from the mouth of the Lord. Also in Jeremiah 31:34 it says, No more shall every man teach his neighbor, and every man his brother, saying, ‘Know the Lord, ’ for they all shall know Me, from the least of them to the greatest of them, says the Lord."
So, while devotions and books and commentaries are helpful, they aren't necessary to knowing the Lord. I would encourage you to read your word every day and add those other things like you would a supplement.