The reason why saying "There is a God and He instilled..." is harder than saying "I believe that there is a God and He instilled..." is because the words "I believe that" are weasel words. The literal meaning of "I believe that" is irrelevant; any other weasel words would have the same effect. Consider the same sentence, but replace "I believe that" with "It is likely that", or "Evidence indicates that", or any similar phrase, and it's just as easy.

Just because people are aware of a concept, and have words which ought to refer to that concept, does not mean that they consistently connect the two. The best example of this comes from the way people refer to things as [good] and [bad]. When people dislike something, but don't know why, they generate exemplars of the concept "bad", and call it evil, ugly, or stupid. This same mechanism lead to the widespread use of "gay" as a synonym for "bad", and to racial slurs directed at anonymous online rivals who are probably the wrong race for the slur. I think that confidence markers are subject to the same linguistic phenomenon.

People think with sentences like "That's a [good] car" or "[Weasel] God exists". The linguistic parts of their mind expand them to "That's a sweet car" and "I believe God exists" when speaking, and performs the inverse operation when listening. They don't think about how the car tastes, and they don't think about beliefs, even though literal interpretation of what they say would indicate that they do.