God is shaping the perfect figure of you into what will be your resurrected body and glorified soul. You’ve been sanctified positionally so the sanctification of your person is sure to continue until it’s completion.
Think of a cup being filled to the brim—or inflating a children’s play castle or a basketball to its entire design. The thing being pervaded is what it is, but it is in the process of functioning fully and living up to its potential and peak performance until completely full.
Such gets at the sense of the Hebrew for “perfect” in Psalm 138:a[1], which reads, The LORD will perfect that which concerneth me. David takes consolation in the idea that God will completely fulfill him and accomplish His purposes in him toward his chief end. The text teaches that our perfect God will perfectly perfect His people. So Paul writes in 1 Thessalonians 5:24, Faithful is he that calleth you, who also will do it.
God never discards His people as unfinished projects. First Corinthians 1:8 reads, Who shall also confirm you unto the end, that ye may be blameless in the day of our Lord Jesus Christ.
What is the basis of this profound assurance that Christians will undoubtedly have fought the good fight and finished their race? The second part of Psalm 138:8 tells us: … thy mercy, O LORD, endureth for ever. God’s mercy, ḥesed in the Hebrew, is a word pregnant with promise expressing His covenant loyalty to His people. It is used in Psalm 136 at the end of each of twenty-six verses as a corporate, antiphonal exclamation.[2] God’s faithful covenantal mercies are new every morning (Lamentations 3:22-23). So Christian, you can never lose your salvation and you will grow in your sanctification into the perfect you in Christ. In answer to the last part of Psalm 138:8, Jesus says He will never leave you nor forsake you (Hebrews 13:5)![3]