Why will believers not receive their reward until the end of time?
Believers' reward is delayed to the end of time because, while they live, they keep making impacts on people all around them. That influence is ongoing, so judgment and reward are reserved until the Lord comes, not before the time.
Les explains that in this section Paul is again defending his apostleship. Some in the congregation said they listened to Peter or Apollos, and Paul had to answer that he is judged by no man except Jesus Christ, who sent him as the apostle of the Gentiles. Coming to verse 5, Paul writes, “Therefore judge nothing before the time, until the Lord come.” Les then asks why believers never receive their reward until the end of time, and notes that the lost also do not receive their just recompense until the end of their time. The reason given is that as believers go through this life, they are making impacts on people all around them. Their lives are still affecting others, so the Lord’s judgment and reward await the end, when He comes.
Therefore judge nothing before the time, until the Lord come, who both will bring to light the hidden things of darkness, and will make manifest the counsels of the hearts: and then shall every man have praise of God.