Perjury is the criminal offense of knowingly making a false statement under oath about a material fact. Not every falsehood offered as testimony under oath is perjury. Perjury has three motivations:
Conscious perjury is a sin.
See Exodus 20:16 with multiple commentaries "Thou shalt not bear false witness against thy neighbor." Compare John 8:44 with multiple commentaries "The father of lies".