Seeing that ye have put off the old man with his deeds. Your former corrupt and evil nature. See Barnes "Eph 4:22".

The reason for putting away lying, stated in Eph 4:25, is, that we "are members one of another"- or are brethren. The reason assigned here is, that we have put off the old man with his deeds. The sense is, that lying is one of the fruits of sin. It is that which the corrupt nature of man naturally produces; and when that is put off, then all that that nature produces should be also put off with it. The vice of lying is a universal fruit of sin, and seems to exist everywhere where the gospel does not prevail. Comp. See Barnes "Tit 1:12".

There is, perhaps, no single form of sin that reigns so universally in the heathen world.