Jesus delved into the spiritual and relational responsibilities of His disciples (us), and told them that what causes people to stumble was about to come. Jesus was speaking to future leaders of the church. Moreover, stumbling blocks will be placed along our paths, which will hinder us. But, woe to him/her who would hurt and destroy anyone who recruits a child of God to sin. So, watch yourself. 

Pay attention to yourselves. What goes around comes around. If anyone treats another badly, they will be treated the same way. The scriptures tell us that whatever one sows, he/she will also reap. They tell us that whoever digs a pit for someone will fall into it themselves. Our wicked actions often lead to negative consequences, so treat individuals with compassion for it is returned.