Pursue what is pure
Purity is an increasingly rare thing. Many of our foods are contaminated with filler and unnecessary byproducts. 45% of our nation's tap water and all rainwater is contaminated by PFA's and toxic forever chemicals. You could easily wear yourself out in a vain attempt to find anything pure in this world.
Go into the moral realm and it gets even more murky. Moreover we sinners are experts and taking what is holy and pure and twisting it for our own sordid ends. How can anyone know what is really pure and worth pursuing? Only God can give us the wisdom and insight to know and seek what is truly pure and beneficial for us here and eternally.