After the Akeidah we are told (22:20) that Avraham was informed that his brother had had twelve children and one grandaughter (Rivkah). It takes several years to have that many children, so it would seem that Avraham had not kept in contact with his family all this time to even know that they had had kids. Why was this so; a man who
kept up with the entire world to spread HaShem's light to people could not keep in touch (let alone influence) with his own family?
The Netziv (22:20) explains what is going on. When HaShem told Avraham at the start of Lech Lecha to leav his family this meant to sever all connections to his family; they were too bad an influence on him. However, after the Akeidah Avraham had reached a high enough spiritual level that he would not be influenced by his family, and so he re-contacted his family and found out about their news from over the years.
The lesson? Be wise enough to know that you are not always strong enough to resist being influenced negatively by others.