Too often writers want to preach or demand that people think as they do, but good devotionals carry a sharing tone. Think of two friends talking and one says, "I'd like to tell you an invaluable lesson I learned last week." That's the way you want to write.
Lack of preaching also means you want to avoid words that lay guilt on readers such as should, ought, and must. Steer away from absolutes such as always, ever, and never unless you mean without exception.
Insecure writers tend to write with absolutes.
Resist doing that.