Amazing how a simple teaching of Scripture can be so misunderstood and made complex by so many, even from someone who claims to be a teacher of the Bible!
The answer to the question of the OP is verse 15. However, the context of 1 Corinthians 3:8-15 is found in verses 5, 6 where we find the key words, “ministers,” “planted,” “watered,” and “increase.”
8) “he that planteth” and “he that watereth” are one that is, in harmony, not competition. IOW, the believers are the builders.
9) “we are laborers” = we are builders with God; “husbandry” = field.
10) self explanatory.
11 ) “There can be no other foundation laid” than that of the Lord Jesus Christ. Anyone who preaches another Jesus than that of the Bible let him be accursed, we read!
12) if any man build upon the foundation (Gospel) “gold, silver, precious stones,” “wood, hay, stubble”:
13) Every believer’s work shall be revealed by fire of what sort it is, either saved as gold, silver, precious stones, or unsaved as wood, hay, stubble.
14) If isolated from the rest of Scripture, it seems we will receive a reward. But this verse must be read in light of Luke 17:10; 18:29-30 (in this life).,
15) If a believer’s work is burned he shall suffer loss, but his salvation will still remain intact.
Why? Because all believers have been given eternal life upon conversion and has been mandated by Christ to go into all the world to preach/witness (work) and make disciples of men.
Therefore, the gist of 1 Corinthians 3:1-15 is the “work” or task of all believers to preach and witness as per Matthew 28:19!
And, if he doesn’t lead anyone to salvation, it is no big deal, because it is God who increases and does the saving! Romans 10:17
To God Be The Glory