"Fight the good fight for the true faith. Hold tightly to eternal life to which God has called you, which you have declared so well before many witnesses." 1Tim 6:12.
There are good fights and there are bad fights. Every fight aside fighting to uphold your faith is a bad fight. Fighting for selfish ends, fighting simply so no one looks down at you is not a good fight.
Prioritize on and concentrate on the fight for your faith.
Paul also says; ''hold tightly to the eternal life to which God has called you."
Timothy was not just a believer, he was pastoring this church, yet Paul tells him to hold on tightly to something he should already have.
Can believers lose their faith? If you want to put it differently; can a believer lose the eternal life Christ promised us? From Paul response, if they are not careful to hold on to it, yes, they can.