Why do you use a buffer when the whole point of op amp is to amplify signal?
There are several ways to "amplify" a signal, not only its amplitude is important. Buffers essentially amplify "current", or "input power". They typically have a very high input impedance and low input capacitance, so they don't load much the signal source even at high frequencies. At the same time they have a fairly low output impedance (typical target is 50 Ohms), so they can drive coaxial cables and "deliver" the signal over fair distances without distortions, like in "active" oscilloscope probes. This the the main purpose of "buffers".