[R] what is the difference between using function predict() and coef() in prediction

[tony333]

X8 = c(0.42808332,  0.14058333,  0.30558333,  0.09558333,  0.01808333,
-0.09191666, -0.11441666, -0.12941666,  0.13808333, -0.31691666,  0.25308333
,-0.20941666 ,0.02808333, -0.04441667, -0.43691666)   

xy.lm =  lm(Y~X8)
z = predict(xy.lm,list(X8=X8))
sz = coef(xy.lm)[1]+(coef(xy.lm)[2])*X8
is the same result in this step 
but when use the prediction as 
T8=c(-0.05691667, -0.09441666 , 0.31308333 ,-0.59941665 ,-0.33941666
,-0.64441665,-0.55691665 ,-0.01191667  ,0.22558333, -0.30691666  ,0.97808331
, 0.49808332,-0.30941666  ,0.41808332 , 0.42308332)

zz = predict(xy.lm,list(T8=T8))
ss = coef(xy.lm)[1]+(coef(xy.lm)[2])*T8
here gives me different  value and  zz = z = sz i do not know the reason for
that 
what i understand about predict() act exactly like using coef() but now do
not know  the difference
thank you for respond  

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