. . . [I]f you and I are to wrestle triumphantly against the devil and all his powers, the first essential is assurance of salvation. There is no hope for us in this conflict unless we know God’s power and God’s might. But if we are uncertain about our relationship to Him we cannot stand and withstand in the fight. In other words the key to victory over the devil is assurance of salvation, certainly concerning our relationship to God in Jesus Christ. That is but another way of saying, ‘They overcame him by the blood of the Lamb, and by the word of their testimony.’ You cannot give a testimony if you do not know your position. It is only one who is certain who can give a testimony, and who can act as a witness. The saints’ testimony in the Book of Revelation is that the blood was on them, that they belonged to Christ; they possessed assurance of salvation.
By assurance you are made ‘strong in the Lord, and in the power of his might.’
—D. M. Lloyd Jones, The Christian Soldier: An Exposition of Ephesians 6:10 to 20, 62
Are you certain that you are saved?