1 Corinthians 3:15 (a) This word is telling us that the believer's life should be filled with profitable and useful works so that he will receive a full reward at the judgment day. It has no reference whatever to the salvation of the soul. It refers only to a failure to receive a reward for faithful service. It is the reward that is lost, not his soul.
Philippians 3:7 (b) Paul indicates plainly that all those religious observances which he practiced before he was saved, before he met the Lord JESUS, were only a liability to him, and not an asset. He was glad to get rid of all his beliefs and practices as a Pharisee in order that he might enjoy the liberty and the loveliness of CHRIST JESUS, his new Lord. The old things as a Jew were a liability to him. The new things as a Christian were an asset to him.