It was many years ago that I was taught that, when one reads the word "therefore" in the Bible, one should ask "What is it there for?" In those words, it refers to all of the teaching that Paul has previously provided to the recipients. It is, indeed, the pivot word on which this section of Romans turns from belief to behaviour. Up until this point, Paul has been explaining what God has done to redeem us. He now challenges his readers (now, as well as then!) to surrender themselves, totally, into God's hands.
Self-surrender and self-sacrifice have, of course, been demonstrated by God before He demands them from us! Tomorrow (Saturday) is, of course, the Jewish Shabbat. Judaism has its own "lectionary" - set readings from the Scriptures for each week, or even day. In synagogues around the world, one of the passages that will be read on this particular Shabbat is from the Book of Leviticus: "Speak to the sons of Israel and say to them, ‘When any man of you brings an offering to YHWH, you shall bring your offering of animals from the herd or the flock. If his offering is a burnt offering from the herd, he shall offer it, a male without defect; he shall offer it at the doorway of the tent of meeting, that he may be accepted before YHWH." (1:2-3). The Hebrew word korbanot means to be close and the point is that the sacrifices, once accepted by God, restore closeness and intimacy between Him and His people. Why is this necessary? Because our iniquities and sins separate us from God and prevent us from establishing or maintaining a close relationship with Him. "But your iniquities have separated you from your God; your sins have hidden His face from you, so that He will not hear." (Isaiah 59:2). For we who live under the New Covenant, the perfect sacrifice was made by God Himself, in the Persona of the Son.
It is our sin - yours and mine - that took Jesus to the cross in the greatest act of self-sacrifice in all of history. When He asks us to surrender ourselves, He is not asking us to do, or give, anything that He has not already done, and given.
The story is told of a missionary who shared this truth with a highly intellectual Hindu, and added, "I believe that to be the high watermark of the universe". The Hindu removed his spectacles, wiped away an involuntary tear, and replied, "High watermark? That's the highest watermark of which the human mind could ever conceive!" How true! In the self-giving of Himself, Almighty God set the standard for the universe. Nothing in either God, or in man, can ever go beyond it. It is the highest truth conceivable.
Have you submitted yourself to Him? Have you presented yourself, a living sacrifice? It is, indeed, no more than "reasonable service"!