And receiving the helmet of salvation ... (Ephesians 6:17a).
The helmet of salvation pertains to our salvation. Satan does not want us to be stable in our belief concerning salvation. He will attempt to influence us to question whether we are truly saved or persuade us to add something in order to ensure we remain saved. If he can, he will even seek to convince us that we must maintain our salvation through works.
Salvation is based upon faith. Faith is taking God at His word. It is not of works (Ephesians 2:8–9). God is the One who sought us, and the Holy Spirit is the One who convinced us of the truth (Romans 3:11; John 16:8–9). Through God’s mercy—by the washing and regeneration of the Holy Spirit, not by works of righteousness which we have done—we are saved (Titus 3:4–5); therefore, salvation is a work of God, not of man. It is not by man’s desire or effort, but by God’s mercy that we have salvation (Romans 9:16). We do not begin in the Spirit to be made complete by the flesh (Galatians 3:3). God has stated that He will never leave us nor forsake us (Hebrews 13:5). Since it is impossible for God to lie, our salvation is as secure as His word (Titus 1:2).
With the helmet of salvation, we can overcome disappointment (Romans 5:5), discouragement (Hebrews 12:3–5), spiritual cowardice (Luke 22:31), and an ungracious spirit (2 Corinthians 2:10–11).