I spent 16 years serving as a protestant minister in a few different denominations. I suppose I was a bit stubborn in converting to Catholicism. Down through those years I encountered various people who influenced me towards the Catholic faith--not Catholics (I knew very few of them), but protestants (yes, you read that correctly).
Some of those protestants who helped me to become Catholic, did not even know they were doing so. It was usually people who were merely living out their protestant faith and giving me clear examples of what was wrong with the protestant experiment as a whole. I saw numerous examples of all the most detrimental aspects of non-catholic thinking. It was those things that made me reconsider whether the protestant way of doing things really was working out after all.
Then there were the protestants who had beliefs that fit better with the Catholic faith than with the protestantism they professed. If you look far enough and wide enough you will come across many (but not all) of the Catholic teachings in various places in the protestant spectrum. No one denomination has all of it, but much is spread around. When I encountered those things, I would see their roots in the Church of the first few centuries. That is what made me wonder, if they had those beliefs, why did they let the other early Church beliefs drop.
In the end, there were many non-catholics who helped me become Catholic. I thank God for using those people for my salvation. I thank Him that He can speak through those who do not even fully accept His words. What a tremendous grace that our Sovereign God is able to use anything He wants to help us. If He can speak through the mouth of a donkey, He can certain speak through the mouths of those who are confused about Who He is. Let us be thankful for all those things He uses to guide us in the faith, and ask Him to use us all the more.