From John Pipers series on Battling Unbelief:

Are we not then saved by faith—by believing in Jesus Christ?
We are indeed! Those who persevere in Faith shall be saved (Matthew
24:13; 10:22; 1 Cor. 15:3; Col. 1:23; 2 Thess. 2:13). How do you
lay hold on eternal life? Paul gives the answer in 1 Tim. 6:12—"Fight the good fight of faith: lay hold on eternal life."...

The great error that I am trying to explode in these messages is
the error that says, faith in God is one thing and the fight for
holiness is another thing. Faith gets you to heaven and holiness
gets you rewards. You get your justification by faith, and you get
your sanctification by works. You start the Christian life in the
power of the Spirit, you press on in the efforts of the flesh. This
is the great evangelical error of our day. The battle for obedience
is optional, they say, because only faith is necessary for
salvation...

Our response: the battle for obedience is absolutely necessary
for salvation because it IS the fight of faith...