"But thanks be to God that, though you used to be slaves to sin, you wholeheartedly obeyed the form of teaching to which you were entrusted."
Just a (hopefully) quick thought on this verse. As Christians, we need to "wholeheartedly" obey God, to completely and fully give ourselves to serving him, to give our entire lives to him, as slaves of righteousness (See v16).
Tying that more specifically to the next part of the verse: "the form of teaching to which you were entrusted." How do we obey God? We obey his teaching (the bible) which has been entrusted to us. Entrusted = given, but with trust involved. Like in the parable of the talents (Matt 25:14-30), the tenants are entrusted with money. So, we have been given God's word, what do we do with it? We can either use it or waste it.
Using it would involve using it wholeheartedly, using it as much as possible, reading it, thinking about it, memorising it, talking about it, listening to people explain it (i.e. going to church), and the like. Wasting it (obviously) would be to not read it, to not put time and effort into knowing God's word.
Now, lets compare it to ourselves. We have God's word readily available. We have churches - PLENTY of churches. We are not persecuted, and are hardly even mocked by others for our faith. We do not suffer for it. Yet, how often do we read it? Daily? Weekly? Not even that? Explain to me how that fits with "Wholeheartedly obeying". It just doesn't! We (I included) waste our time so much instead of using it to obey God.
So, what are we going to do about it?
A little bit of a side note: Even if we do that, note the first bit of the verse: "Thanks be to God". We can only wholeheartedly obey God if he by his grace has saved us through Christ Otherwise we are slaves to sin, and deserving God's wrath. So, "repent and believe for the kingdom of God is at hand!" Jesus alone saves, and it is only by his grace that we can get out of sin and obey God. (See the rest of Romans 6). That's what its "thanks be to God. We have nothing to be proud about, even if we are doing the right things - all glory belongs to God!