Summary
Romans 1:28 says that the result of straying from God’s truth is God giving us over to a depraved mind, so that we do that which ought not to be done. It should rightly frighten us that God will give us over to a depraved mind if we turn away from Him, but we do not need to fear what horrible actions we might engage in upon such a path of straying if we choose instead to never stray—walking in the Spirit by always keeping our eyes firmly fixed upon Jesus Christ and the righteousness we have through Him. Then our minds will be renewed by the truth (cf. Romans 12:1-3), rather than becoming filled with depraved desires.
Content
As the verse directly says, the result of straying from God’s truth is God giving us over to a depraved mind, so that we do that which ought not to be done.
We discussed some of mechanics of this already, in talking about how God won’t give up on sinners, but will let people freely choose against Him, hardening their hearts as they ever choose more against Him so that they can pursue their folly without logic forcing them to confront the truth.
We also previously went over the consequences of sin, how sin inherently begets death. That discussion is also relevant here.
It should rightly frighten us that God will give us over to a depraved mind if we turn away from Him. The consequences of such a path are, in fact, a godly way to keep us on the straight and narrow. It seems to me that many find it fashionable to criticize the supposedly “selfish” attitude of turning to Christianity to flee hell. (What is usually pushed instead is how we ought to act “only” out of motivations of wanting to please God). But I don’t see anything in the Bible that condemns taking the carrot (eternal rewards for following God) and stick (eternal damnation) into account when we make decisions. We ought to want to please God too, of course, but the point is more that the things are not mutually contradictory. And this truth—that we can be self-interested while yet at the same time also truly be acting out of a desire to please God—is in fact by the grace of God.
That is, God arranged the world in such a way that we do not even have to go against our self-interested natures to be saved. Submitting to God is actually the logical choice, from the perspective of self-interest! But we do have to not say no. Otherwise, as this verse says, we will face the consequences.