Amos 9:1-4 recapitulates many themes from earlier in the book of Amos for climactic effect and even intensifies these themes. Amos says that a fate worse than death is coming for the Israelites, and this fate is absolutely inescapable.
Whatever strength you feel you possess that you can boast in, God does not think much of it. God is not against your strengths and talents, but when you rely on them rather than on him to secure and defend your prosperity, God says that all your excellence, all that in which you would take pride, is nothing next to his power. Your mighty fortress will not secure you against his justice.