Faith is the only way! To the Old Testament folks it was faith in looking forward to the Coming Messiah whose shed Blood was represented by the blood of an animal sacrifice.
For the New Testament folks it is faith in looking back at the Messiah and the Blood He shed for us.
So you say "believe only" --- belief + 0 = salvation?
Scripture refutes your position...
Mark 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.