Following on from the warning to not put a stumbling block in front of others, comes this related instruction. If you have legitimate cause to admonish your fellow believer, you must still do it with great caution.
You are to forgive, and that means you hold no grudge, and you accept a full restoration of fellowship with that brother. He is a brother and a fellow believer, and you therefore have grounds to hope for better things from him in the future.