Among the identities of the Christian, which are faith, holiness, righteousness, justification, sanctification, etc., faith is the only attribute which is not a constant. Upon regeneration (rebirth) by the Holy Spirit the believer is holy, righteous, justified and sanctified, which are states of being, not doing. The doing (works) will result from these, which are imputed and not imparted (1 Cor 1:30). They are vicariously possessed in us through the life of Christ (Col 3:4) by the Spirit and cannot be produced, thus one can only “bear,” not produce, “much fruit” (John 15:8).
Knowing the responsibility of producing is of God (it must be “worked in you” Phl 2:13) allows us to rest from the needless labors of attempting to bring about that which He supplies. This frees us more to do our part, which is to "labor to enter that rest," e.g. labor to rest, or believe in the sufficiency of Christ's atonement alone for our support, and true godliness will follow—in our works—not by them. Belief which is exercised in anything other than the efficacy of Christ, is an "example of unbelief" (Heb 4:11).
That which is constant (holiness, righteousness, etc.) does not vary in degrees, thus the believer will not be more saved (but more delivered from the body—Rom 8:23) in Heaven any more than now, as is the same for all of the remaining Christian attributes. One cannot be more holy or righteous now than at the time of regeneration because these are immutable (Rom 11:29), being imputed from Christ. Can He be more holy or just? “As He is, so are we” (1 John 4:17).
It is the grace of faith that progresses (1 Pet 1:5-7) from these imputed attributes, as the Spirit incrementally “changes” the believer “from glory to glory” (2 Cor 3:18)—without end. Some have the idea that sanctification is a variable because they relate it to that of doing instead of being, but this attribute is always in the present tense and is, as the others are, a single occurrence at rebirth.
As that which is imputed is more understood and learned of by the Spirit, that which is not a constant (faith and works) will continue to increase for the purpose of showing or "glorifying" the life of Christ, thus fellowship, worship and service will attain an ever increasing pace.