Plucking, pruning, trimming, tweezing

Maintenance.

That's one constant of this world. One job God gave to Adam was to work in the Garden of Eden, to keep it maintained. Even an unfallen world benefited from maintenance. But after the fall, it needed maintenance.

Consistent work is required to keep many cogs in the machine well-oiled. You can't just buy a car and expect the money you paid at purchase to be the last you will ever pay toward that car. The car requires gas, oil, antifreeze, power steering fluid, wax, etc.

Likewise, we cannot expect the price Jesus paid for us to be with him and in him to be the only sacrifice ever made. Yes, it is sufficient for all. But no, it should not be treated as the be-all end-all of our relationship with him.

In the words of Titus 3:

... Be in subjection to rulers and to authorities, to be obedient, to be ready for every good work, to speak evil of no one, not to be contentious, to be gentle, showing all humility toward all men. 
For we were also once foolish, disobedient, deceived, serving various lusts and pleasures, living in malice and envy, hateful, and hating one another. But when the kindness of God our Savior and his love toward mankind appeared, not by works of righteousness, which we did ourselves, but according to his mercy, he saved us, through the washing of regeneration and renewing by the Holy Spirit, whom he poured out on us richly, through Jesus Christ our Savior; that, being justified by his grace, we might be made heirs according to the hope of eternal life. 
This saying is faithful, and concerning these things I desire that you affirm confidently, so that those who have believed God may be careful to maintain good works. These things are good and profitable to men; but shun foolish questionings, genealogies, strife, and disputes about the law; for they are unprofitable and vain. Avoid a factious man after a first and second warning; knowing that such a one is perverted, and sins, being self-condemned.

We must not return to the foolish, disobedient ways we behaved before coming to Christ, but in honor of His sacrifice, struggle to be gentle, humble and peaceful toward all. Doing good will certainly not save us, but will maintain our faith, just as a new outfit still requires cleaning so that it doesn't become dingy, or a new mirror still needs to be dusted or it will not reflect as clearly.