To assume that remaining in the book of life rests upon continuing loyalty to Christ ignores the fact that before all human faith or striving lie the divine choice and the divine initiative. The worthiness of the faithful . . . is based on divine grace (cf. Rev. Rev. 7:14+). It is incomprehensible that it could be lost through human unfaithfulness. Couple with these considerations the fact that Ps. Ps. 69:28 has the names of the wicked in the book of life, and the basis for an assumption that [being blotted out] refers to a loss of ones salvation is eliminated.2Thus, the warning Jesus gives to the church at Sardis (Rev. Rev. 3:5+) is an admonition to those who are not yet overcomers to become overcomers or else their names will be blotted out. The double negative found there, οὐ μὴ [ou mē] , indicates that those who overcome will never be blotted outwhich is the substance of the promise Jesus makes.
1 Concerning the security of the believer, see: Luke Luke 10:20; Luke 15:21; John John 3:36; John 5:24; John 6:39, John 6:47; John 10:28-29; John 17:12; Rom. Rom. 8:29-30; 1Cor. 1Cor. 1:7-8; 1Cor. 10:13; 2Cor. 2Cor. 1:21-22; Eph. Eph. 1:13-14; Eph. 4:30; Php. Php. 1:6; 1Th. 1Th. 5:23; 1Ti. 1Ti. 1:12; Heb. Heb. 7:25; Heb. 10:14; 1Pe. 1Pe. 1:3-5; 1Jn. 1Jn. 2:19; 1Jn. 5:13; Jude Jude 1:1; Jude 1:24; Rev. Rev. 7:4+; Rev. Rev. 14:1+.