When there is a vacuum in our souls
In "God's Word for Today" Gordon Snider writes:
If there is a vacuum in our souls, however, covetousness will fill it! So having warned us against its danger, Paul urged the believer to fill the soul with higher qualities (v. 11)! To do so requires strenuous effort — active engagement (v. 12). People who live on with this world in view will succumb to the temptation of covetousness (vs. 7, 14-16). That is how Jesus avoided the materialism of His day (v. 13). He focused, not upon His standing before His peers, but upon His standing before His Father. Living in the presence of God lessens the attraction of earthly valuables! Paul wanted to make it clear, however, that possessions are not the danger, but our attitude toward them. He assumed that some people will be entrusted by God with greater wealth than others. Being so entrusted, however, can prove to be our damnation unless we develop and live by a godly theology of abundance. A key component of such a theology is a spirit of giving. If those who are blessed with this world's goods have truly learned the dignity of all humanity, they will find that they will want to enable the less fortunate.
Source: Building Christian Relationships: Adult Teacher's Insights, page 29.