I’ve suggested that the “enemies of the Cross” that Paul is referring to are those who add rituals, customs, performances or sacrifices as necessary ingredients to salvation. If the Cross is not 
sufficient in and of itself then whatever must be added becomes a “work” which saves us. This contradicts the major teachings of the New Testament that “it is by grace you are saved, through faith. It is a gift of God, not of works, lest any man should boast” (Ephesians 2:8-9). But when Paul goes on in Philippians 3:18-19 to describe these enemies of the cross he says, “Their end is destruction, their god is their belly, and they glory in their shame, with minds set on earthly things.” Many misunderstand this passage. They say it pictures the enemies of the cross as sexually immoral, gluttons, whose only interests are the pleasures, possessions and privileges to be had in this world. The “end” of such people may very well be “destruction.” But that destruction will not be because of their immorality or gluttonous behavior. It will be because they did not avail themselves of the grace of God offered at the cross of Calvary.
What does it mean to have your belly be your god? I’d argue that this is a reference to the Jewish ritual eating habits. When Paul wrote to the Corinthians he had a large section dedicated to eating habits. When God called Peter to go to Cornelius’ house, Peter wouldn’t go because of the pagan eating habits. But God showed him three times that all foods are clean. In Mark 7:18-19, Jesus was doing battle with the religious leaders who attacked him for what Jesus may have eaten. He says, “Do you not see that whatever goes into a person from outside cannot defile him, since it enters not his heart but his stomach, and is expelled?” The most important part of this passage is what follows. Mark adds a meta-comment. He said, “Thus he (Jesus) declared all foods clean.” In Romans 16:17-18, Paul is again doing battle with those who are upsetting the believers with their teachings about legalistic observations. He says, “I appeal to you, brothers, to watch out for those who cause divisions and create obstacles contrary to the doctrine that you have been taught; avoid them. For such persons do not serve our Lord Christ, but their own appetites.”
The next phrase in the Philippians passage says that the enemies of the cross “glory in their shame.” Moises Silva, in his exegetical commentary understood that the Greek word for “shame” has been “interpreted with specific reference to Jewish practices. According to this interpretation, the term alludes to the sexual organs and thus indirectly to circumcision.” At the beginning of Chapter 3, Paul made it clear that the circumcisions of the legalists were actually their mutilations. Their mark of pride became their mark of shame! Paul counted his own circumcision as rubbish. Finally, the passage says their “minds are set on earthly things.” Paul’s mind is on the “upward call of God.” His whole purpose and passion in life as expressed is clearly to know Christ and the power of His resurrection. Earthly things are rituals, rules, and religion!