In Romans 1:9-10 Paul says, “For God, whom I serve (λατρεύω) in my spirit (ἐν τῷ πνεύματί μου) in the gospel (ἐν τῷ εὐαγγελίῳ) of his Son, is my witness as to how unceasingly I make mention of you, always in my prayers making request, if perhaps now at last by the will of God I may succeed in coming to you.”
This statement intrigues me for three reasons:
(1) The word λατρεύω can be used to depict cultic worship or temple service. In 9:4 Paul says that one of the things Israel received was ἡ λατρεία, translated “the temple service” (NASB), “the worship” (NRSV), or “the temple worship” (NET). In 1:25 rebellious humanity is described as worshiping (ἐσεβάσθησαν) and serving (ἐλάτρευσαν) the creature/creation rather than the Creator. Interestingly, Paul makes a distinction between one form of religious veneration and another, the second (ἐλάτρευσαν) which he seems to affiliate with formal cultic worship in 9:4. I haven’t done an extensive word study, but it may be that in this epistle latre- words have the connotation of cultic worship (if anyone has done a study on this let me know what you’ve found).
(2) The first prepositional phrase in 1:9 is the dative “in the spirit” (ἐν τῷ πνεύματί) with the genitive pronoun “my” (μου). I presume Paul means something like “in my inner person” though I recall Gordon D. Fee’s various studies on Pauline Pneumatology did present a very thin line in Pauline thought between his own human spirit and the divine spirit. The question that emerges here is “Why does Paul classify his act of worship?” Does Paul want to make a distinction between this worship and the worship of Israel as described in 9:4, or the worship of rebellious humanity in 1:15, or both?
(3) The second prepositional phrase in 1:9 is the dative “in the Gospel” (ἐν τῷ εὐαγγελίῳ) with the genitive “of his Son” (τοῦ υἱοῦ αὐτοῦ). Now Paul’s worship has two qualifying descriptions: “in my spirit” and “in the Gospel of his Son”. As with my second observation I wonder why Paul demarcates his worship as having these two characteristics.
Is Paul aiming to differentiate his worship from other approaches to worship? If so, why?
the archives near Emmaus 
The climax of Romans 1 is a condemnation of the Israelites who departed from the Law that had been given to them (most likely around the time of the Golden Calf, but possibly including their immorality since then). I think it’s likely that Paul was indirectly claiming that his method of worship was superior to that of the Jews in his generation since their Temple worship had become idolatry.