As a result, we are freed from the trap of beginning with grace and finishing by works. Too many of us are tempted to believe that, while God has saved us and may be pleased with us, he would be even happier if we were missionaries or pastors, if we could do some extraordinary service for him. Then, we mistakenly believe, then God would be satisfied with us. But this perspective fails to understand two important truths. First, we are still, at best, sinners saved by grace. We confess that our best works, which proceed from God's Spirit, "are defiled, and mixed with so much weakness and imperfection, that they cannot endure the severity of God's judgement" (WCF 16.5). Second, God is not satisfied with us because of what we have done or can do. In fact, we can't do anything that would satisfy God. We believe that "we cannot by our best works merit pardon of sin, or eternal life at the hand of God" (WCF 16.5). Rather, God is satisfied with us only because he sees the perfect work of his Son. Because our persons are "accepted through Christ, their good works are also accepted in him; not as though they were in this life wholly unblamable and unreprovable in God's sight; but that he, looking upon them in his Son, is pleased to accept and reward that which is sincere, although accompanied with many weaknesses and imperfections" (WCF 16.6). Even as Christians, our best works are accepted only by virtue of our union with Christ; God continually looks at us in his Son and thereby accepts our works as flawed as they are. We begin by grace and we continue by grace.
--Sean Michael Lucas, On Being Presbyterian