I think it's not quite as simple as that...
A lot of people trust Him for their salvation but then get it a little messed up for a while, just like the Galatians did, by thinking they then have to make themselves holy somehow. And they have to find out the hard way that they can't. That there is something in them that makes them do what with all their heart they don't want to do. I used to murder everyone I came in contact with. I am not exaggerating the point. I was constantly angry at their demands of what I do for them but then when I needed help, they were so selfish and there was no help to be found. If anyone didn't rinse off their plate and the food and cheese was caked on the next morning, I would scrub and murder, scrub and murder, rinse and repeat. And when I saw I had failed, despite my best efforts and had murdered again, I would fall into depression at being how I didn't want to be. And when I would cycle up out of my depression, I would resolve to try harder. And then the cycle began again, always ending in my failure to be holy in my heart. I was allowed to go on this way for years until one day I said, I give up. I cannot do it. If it's to be done, you have to do it Lord, please have mercy on me! And I very quickly began to have great victory over my murdering in spirit.
So what I'm trying to say is...it is possible to have trust in Him in one area but rely on your own strength in another. It is possible to firmly believe some of what He said and promised and to be in some mistrust and unbelief in some other thing He promised. We grow in our trust (faith). It's a race of trust and the more that trust is excersized through trials of trust, the stronger it grows.
