Yes, it looks like each of your rows  in Sheet 2 is unique, with 4
columns in each. My advice would be not even to think about VBA, but to
use VLOOKUPs to read the information straight onto Sheet 1 in the 3
additional columns, in the format below for Sheet 1 B1:

=VLOOKUP (A1,Sheet2!A1:D40000,1,TRUE)

For columns C and D replace the ,1,TRUE with - respectively - ,2, TRUE
and ,3,TRUE. The select B1:D1 and drag down the length of the range to
row 4000.