"... I persecuted the church of God and tried to destroy it.  I was advancing in Judaism beyond many Jews of my own age and was extremely zealous for the traditions of my fathers." - Galatians 1:13-14

Okay, so he wasn't doing exactly what God wanted him to do, but when Saul was going after the Christians of his time, he genuinely thought he was doing right by God.  He was surpassing the other pharisees his age and he was "extremely zealous" in his spiritual pursuits.  After all, it was for God he was persecuting the blasphemers who claimed God had been crucified.  He knew that couldn't be possible because he knew what the scriptures about the Christ to come, and he'd left himself open to hearing and knowing God's will.

How do we know he left himself open to God's will?  On the way to Damascus, Saul had a vision of Jesus that changed his life and showed him that he'd been on the wrong path.  This wouldn't have happened if God didn't think there was something redeemable about this killer, and it couldn't have happened if Saul hadn't been seeking God.  God won't force Himself into our lives, but He waits for us to invite Him in - and He will enter.

Saul had been on the wrong path, but for the right reasons.  God turned this Jewish killer into the Apostle to the Gentiles.  He can do the same with us.  If we are willing to follow God wholeheartedly, and we seek to know what His will is, He'll steer us in the direction He wants to send us, and reveal Himself to us in a life-changing way.  Don't be afraid of moving in the wrong direction because "God works for the good of those who love Him" (Romans 8:28) and He will use us - sometimes despite ourselves.  Check your motives and move forward, trusting God to direct your path.