Excursus--"Spiritual Worship" in Rom. 12:1
The idea of "worship" is introduced at the end of Rom. 12:1, but there is a wide range of opinion on how to translate 
, which is not in the LXX and appears elsewhere in the New Testament only in 1 Pet. 2:2. Classical usage makes it the adjectival cognate of 
, suggesting the translation
"rational".
Moulton and Milligan argued for "metaphorical" with some textual evidence (ibid., 129), and idea that works well here. Modern translations (NIV, NRSV) of 
have
"reasonable worship"
as a second meaning, which, of course, is "true" worship which is thus "spiritual worship," which they place as the first meaning, but "rational" is the least interpretive and therefore probably best translation.
Although attempts to render the phrase in English greatly vary ( Fitzmyer, "as a cult suited to your rational nature" ), there seems to be agreement that Paul is juxtaposing the empty sacrificial worship of pagans which results in dead animals with the true sacrificial worship of the Christian believer, which is to make one's life as a living sacrifice. The former requires no commitment, the latter requires complete commitment.