God did not call us to uncleanness, but in holiness. 1 Thessalonians 4:7 (NKJV)
You are born again by God’s Spirit when you believe in Christ’s atonement for your sins. That is salvation, a singular decision with eternal permanence.
You are also sanctified by the same Spirit of God. But unlike salvation, sanctification is a lifelong process. In The Pursuit of Holiness, Jerry Bridges describes the joint venture of holy living:
The farmer knows that unless he diligently pursues his responsibilities to plow, plant, fertilize, and cultivate, he cannot expect a harvest at the end of the season. In a sense he is in a partnership with God and he will reap its benefits only when he has fulfilled his own responsibilities. Farming is a joint venture between God and the farmer. The farmer cannot do what God must and God will not do what the farmer should do.
We can say just as accurately that the pursuit of holiness is a joint venture between God and the Christian. No one can attain any degree of holiness without God working in his life; but just as surely, no one will attain it without effort on his own part.