What I talk about here is the difference between real Christians and those who merely profess their faith in Christ (and they are NOT Christians). For us to be sure we are Christians, there are scriptural warnings and exhortations to holy life so, if we heed to them, we can know we belong to Christ forever. (That is how we can have assurance of salvation.) Since it is possible that we do not have saving faith in Christ at all and there are many false believers out there, it is important that we follow Christ, so we can be sure from time to time that we are saved. However, we can go astray sometimes, but It does NOT mean we can lose salvation. Once we are saved, we are always saved (OSAS) since God is perfect and His work of salvation which He provides to us who believe is perfect and wholly satisfactory. To God be the glory forever!