Are Christians still under a required ritual of worship?
No. Christians are not under any required ritual of worship. Romans 12 describes the believer's service as intelligent, logical, practical, and lived out by presenting the body as a living sacrifice, holy and acceptable to God. Such service is not ritualistic; believers are set free from commanded ceremonial forms.
Les explains the contrast between ritual-bound worship and the believer's liberty. He notes that a visitor at a Roman Mass or Jewish synagogue service may be confused because the established ritual dictates when to stand, kneel, sit, or respond. But Romans 12 uses the same service word, latria, yet with the Greek word logike, translated intelligent. Les says this means the Christian's service is not divine or ritualistic or religious in that ceremonial sense, but intelligent, logical, or practical. The believer presents the body as a living sacrifice, holy and acceptable unto God. Les emphasizes that we are no longer under demands of a certain ritual, saying, “You'll do it this way, and this way, and this way.” Instead, we're set free and not under any particular commanding type of ritual.
I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service.