Romans transitions from teaching us about the things God has done for us to giving practical instructions for how we should live. It all starts with giving ourselves as living sacrifices and being completely transformed. The idea of a sacrifice refers back to when animals were sacrificed to various gods. Once we have given ourselves as a sacrifice, we are able to humbly operate as a gift to others and to love others in self-sacrificing ways.
There is an old saying that the problem with being a living sacrifice is you can still crawl off the altar. We can decide at one point we want to submit everything about ourselves to God and then later take some of the control back. That will be a struggle for everyone while on this earth, but recommitting ourselves to God is something we can do today.