Biblically speaking, assurance represents “security of the soul and true inner peace – a blessed assurance.” (Paul Sain) It comes from the Greek, plerophoria , which means “ full assurance, most certain confidence..” (Thayer’s Greek Definitions) In English, the word “assurance” comes from the verb “assure.” Webster’s defines assure, “to make safe; to give confidence to hearts; to make sure or certain: convince; to make certain the coming or attainment of: i.e. a guarantee”
Assurance then is, according to Webster’s Dictionary, “The act or action of assuring: as a : pledge, guarantee” God has pledged, “I will never leave you, nor forsake you…” (Hebrews13:5). By the same Word in which He conveyed to us these great and precious promises, He also gave us all things that pertain to our receiving of these promises. “As His divine power has given to us all things that pertain to life and godliness, through the knowledge of Him who called us by glory and virtue, by which have been given to us exceedingly great and precious promises, that through these you may be partakers of the divine nature, having escaped the corruption that is in the world through lust.” (2 Peter 1:3-4)
Along with the pledge to never forsake us, God has given us the Spirit as a guarantee or earnest of that pledge. The guarantee or earnest of the Spirit helps to instill confidence of salvation in us, even though, “we who are in this tent groan, being burdened…” (2 Corinthians 5:2). The Holy Spirit is God’s earnest or guarantee (I.e. the “down-payment”) whereby He gives us assurance that everything He has promised us is true.
Again, Webster’s dictionary states that assurance is, “The state of being assured: i.e. A being certain in the mind or confidence of mind or manner, freedom from self-doubt or uncertainty.” Although he does not use the word “assurance”, the apostle Paul defines this very beautifully in 2 Timothy 1:12, “For this reason I also suffer these things; nevertheless I am not ashamed, for I know whom I have believed and am persuaded that He is able to keep what I have committed to Him until that Day.”
Assurance is closely connected to faith. Our assurance comes from a deep faith or trust in the promises that God, through His Son, has given us. If we have faith in the promises of God – we can be assured that He will fulfill His promises.