Believers must be constantly on guard against potentially causing others to sin. Ultimately, causing others to sin is to sin against Christ.
The true Christian who harms another believer by causing him to sin invites the severe discipline of God into his life.
Believers must never tolerate personal sin. Instead, they should seek to mortify it on a daily basis by following biblical principles.
Christians must not merely mortify sin in terms of the external realm, although that is absolutely necessary. Christians must deal with sins of the heart, which is the root of external sins.