Problem with the VSURF function for Variables Selection

Hello everyone, I am a biologist student trying to work with R:
I am trying to do Variables selection with the VSURF function.
FinalData<-VSURF(formula=KI67~.,lmerd,na.action=na.omit)
It turns a warning message:
Thresholding step
Estimated computational time (on one core): 68 sec.
|============================================================================================| 100%
Interpretation step (on 12 variables)
Estimated computational time (on one core): between 3 sec. and 57 sec.
|============================================================================================| 100%
Prediction step (on 6 variables)
Maximum estimated computational time (on one core): 16.5 sec.
|============================================================================================| 100%Warning message:
In VSURF.formula(formula = KI67 ~ ., data = lmerd, na.action = na.omit) :
VSURF with a formula-type call outputs selected variables
which are indices of the input matrix based on the formula:
you may reorder these to get indices of the original data

I would like to know what's the problem please.
Thank you very much