Concise Bible Dictionary:

The trust and boldness that faith in God and His word gives. “In the fear of the Lord is strong confidence”; “The Lord shall be thy confidence” (Prov. 3:26; Prov. 14:26). “We are made partakers of Christ if we hold the beginning of our ‘assurance’ firm unto the end” (Heb. 3:14). In contrast to this the “fearful” are classed with the “unbelieving” (Rev. 21:8).