Rom1:5 and Rom16:26 most literally says obedience [] faith. The Greek grammar at it's most base and simplistic is translated as obedience [of] faith because those brackets need to be filled in to make some sense in English. But there are several very specific. legitimate ways to interpret the grammar and fill in the brackets.
This wording "that comes from faith" is one of several ways to translate this and is the favored of the faith-alone advocates who need faith to be alone and separate from all other words that Scripture uses to describe and define genuine faith. This also gives them the root and fruit idea.
But, there are other legitimate ways to translate this phrase:
- obedience [which is] faith, obedience [consisting of] faith, obedience-faith or faith-obedience, obedience namely faith
- Paul will show also in Rom10:16 that he considers faith and obedience to be virtually interchangeable when he's discussing genuine faith - the just above translations are consistent with this.
- Hebrews3:18-19 will also substantiate this.
- Then there are other ways to legitimately translate this phrase, such as: obedient faith or faithful obedience.
Rom1:5 and Rom16:26 being used to substantiate faith-alone theology is not a strong argument. In fact, in light of how Paul uses faith and obedience in Rom10:16, how Heb3:18-19 substantiates Rom10:16, and based upon some other factors I normally add, but am cutting short here because the above is sufficient, IMO using this root and fruit argument is very weak.