"A free will is not the liberty to do whatever one likes, but the power of doing whatever one sees ought to be done, even in the very face of otherwise overwhelming impulse. There lies freedom indeed."
Arminians and Calvinists will argue about to what extent free will is involved in salvation. The theories really don't matter, in my opinion, so, to avoid quarrels and confusion, I will not discuss them. The essence of salvation -- the crucial aspect to understand in Christianity -- is that Christ came to set us free. What does that mean?
Galatians 5:1, 13-18
"It is for freedom that Christ has set us free. Stand firm, then, and do not let yourselves be burdened again by a yoke of slavery.
13 You, my brothers and sisters, were called to be free. But do not use your freedom to indulge the flesh[a]; rather, serve one another humbly in love. 14 For the entire law is fulfilled in keeping this one command: “Love your neighbor as yourself.”[b] 15 If you bite and devour each other, watch out or you will be destroyed by each other.
16 So I say, walk by the Spirit, and you will not gratify the desires of the flesh. 17 For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are in conflict with each other, so that you are not to do whatever[c]you want. 18 But if you are led by the Spirit, you are not under the law."
"So if the Son sets you free, you will be free indeed."
So by the power of the Holy Spirit we can choose whether or not to sin because we have free will to choose to sin or obey God. Christ set us free from ourselves, from the law, from others. True freedom is only found in Jesus Christ.