“With a spirit of fervor sustain me” (v12) (New American Bible - NAB)

“Sustain in me a willing spirit” (New Revised Standard Version - NRSV)

“You desire truth in the inward being” (v6a) (NRSV)

“Indeed you love truth in the heart” (NAB)

“Therefore teach me wisdom in my secret heart” (v6b) (NRSV)

“Then in the secret of my heart teach me wisdom” (NAB)

“Truly you are a hidden God” (Isaiah 45.15)

Not “with you God is hidden” as in the NAB and which the NJBC speaks of.  Also from NJBC: “God’s redemptive acts are concealed within human instruments, even within the pagan Cyrus.

“Those go in disgrace who carve images” (45.16)

Once again the theme of the hidden God, whose presence is seen only by faith, as compared to the alternative: those who scorn faith, attempt direct vision, and end up worshipping idols.

“They are without knowledge who bear wooden idols and pray to gods that cannot save.” (Isaiah 45.20)

Faith is the surest type of knowledge.  A study of epistemology reveals this.