“But where has God’s Word commanded us to preach straight through books of the Bible? And who is some pastor or session to impose 5 years’ worth of Sundays through Romans upon your conscience?”
For those who make this argument, it is a simple category error. We who believe in the Regulative Principle of Worship, namely that God alone instructs us how to glorify and enjoy Him, are arguing that there is freedom where the Word of God has not given us explicit direction. The fact is: The Bible does not tell us what to preach when. It is also a gross historical error to assert that “the Church has always marked time through an annual cycle in the life of Christ.” The church calendar was very a long time in developing and there are many different versions of it. Ought we to celebrate the Feast of the Assumption of the Blessed Virgin Mary on August 15th? How about the Calendar of Saints? At any rate, when proponents of the church calendar try to reverse the argument against us who hold to the Regulative Principle of Worship, the argument becomes unintelligible. How can the practice of biblical freedom regarding what passages of Scripture we preach on ever be construed as a violation of conscience? You are, in fact, comparing apples and oranges. Think of it like this: One man is in prison and another is free. Someone then asks: "Who do those police think they are to shut that man up in prison?" And then another man asks, "Who do those police think they are to impose freedom on that other guy?" The first question would get a response. The second question is, well, just weird. It would be like walking up to someone walking down the street in town on a Saturday afternoon and asking them: "How does it feel to have your conscience violated by the police who are imposing freedom on you?" The person would likely be rather bewildered by such a question and rightly so!
Proponents of the church calendar are arguing for restriction where the Bible gives us no such restrictions. This is a violation of conscience – clearly. To argue that by exercising freedom where the Scriptures do not impose specifics we are violating people’s consciences is quite simply wrong. No one’s conscience is violated when Scripture is being followed correctly. That’s the entire point of the Regulative Principle of Worship. The idea that we as a session would impose things upon the people of God which He has not commanded us such that they were left scratching their heads with their consciences wounded thinking, “Should we really be doing this?” is almost more than I can bear as a shepherd. The church calendar is not biblical. Its proponents know this. This is why they will offer nothing from Scripture to support it. Individual churches are free to emphasize and preach and teach on certain parts of God’s Word as they see fit and as their congregations’ pastoral needs would indicate because God has left them free in this matter.
For those who think their creativity or traditions are on par with Scripture, God gave us a haunting warning of His stance toward those who do in worship that “which He had not commanded them.”
Leviticus 10:1-3 Then Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it, put incense on it, and offered profane fire before the Lord, which He had not commanded them.  So fire went out from the Lord and devoured them, and they died before the Lord.  And Moses said to Aaron, "This is what the Lord spoke, saying: 'By those who come near Me I must be regarded as holy; And before all the people I must be glorified.' " So Aaron held his peace.
Deut. 12:32 Whatever I command you, be careful to observe it; you shall not add to it nor take away from it.
It is also important to note that if you accept the argument as laid out at the beginning as a justification for using the church calendar, the same argument can be used to justify almost anything you want. You could make up feast days, festivals, and church calendar days for anything you wanted since no biblical commands or examples are needed to justify them. Anyone who objected that we need some biblical rationale for our practices could then be answered with the above argument. And then: We could have a "Balaam's Talking Donkey Feast Day." And a "David Presenting to Saul 100 Philistine Foreskins Day." As long as we have the same normal elements of worship, we're good, right? And on what possible grounds could proponents of the church calendar object - in principle? Friends, we need to learn to think one step past an initial argument and recognize what, if accepted, it logically leads to.