Once a person is saved, is he always saved?

Once a person is saved, is he always saved?

Jude 5, RS: "I desire to remind you, though you were once for all fully informed, that he who saved a people out of the land of Egypt, afterward destroyed those who did not believe."

Matt. 24:13, RS: "He who endures to the end will be saved."

Phil. 2:12, RS: "As you have always obeyed, so now, not only as in my presence but much more in my absence, work out your own salvation with fear and trembling."

Heb. 10:26, 27, RS: "If we sin deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, but a fearful prospect of judgment, and a fury of fire which will consume the adversaries." (See also Hebrews 6:4-6)