Paul exhorted the Christians in Rome: Παρακαλῶ οὖν ὑμᾶς, ἀδελφοί, διὰ τῶν οἰκτιρμῶν τοῦ θεοῦ παραστῆσαι τὰ σώματα ὑμῶν θυσίαν ζῶσαν ἁγίαν τῷ θεῷ εὐάρεστον, τὴν λογικὴν λατρείαν ὑμῶν· (Romans 12:1 WH)
The operative phrase here is τὴν λογικὴν λατρείαν ὑμῶν. λογικὴν may be rendered as "spiritual" or "logical." The signifier λατρείαν references service that is offered to God. Therefore, the apostle was either telling the Roman Christians to render a "spiritual" or "logical service" to the Most High Deity; but in this context, "logical" seems to be the best choice.
Contexually, Paul is evidently contrasting the sacrifices made under the Mosaic Law with the Christian sacrifice given when a worshiper of God offers himself or herself to YHWH (Jehovah) and His beloved Son. While the animals offered by the ancient Israelites were non-rational sacrifices--the sacrifices being employed under the law of Moses could not reason and they had no choice in the matter--when we offer ourselves to God, it is capable of being and should be a rational decision. But not only should the initial offering be made on the basis of RATIO--Paul also implies that Christian worship, doctrine, and belief should be marked by the quality of rationality. How apt is Anselm's slogan, FIDES QUAERENS INTELLECTUM ("faith seeking understanding"). To put matters succinctly, faith and reason might be considered two sides of the same coin; they are possibly not dichotomous functions of the Christian intellect and will. If a belief is irrational, its validity becomes highly questionable, although we certainly must allow for transrational aspects of true worship since God's thoughts are immensely higher than our thoughts.