Romans 10:11 For the scripture saith, Whosoever believeth on him shall not be ashamed. This is a quote of Isaiah 28:16. Isaiah is referencing the trust Judah had put into their agreements with other nations to protect them from invasion. Paul quotes Isaiah in the context of eternal salvation. Those who believe will not put their trust in other things for their security. Those who claim Christ but later deny Him have either never believed on Him or is acting in contradiction to this passage as they have moved on to put their trust in other things in the midst of their belief. How can anyone believe that a regenerated Christian can ever stop believing?