17 The statement those who have served well as deacons gain a good standing for themselves is reminiscent of Jesus’ teaching (Matt 20:26–28; Mark 10:43–45) that the one who wishes to be great must be a servant (διάκονος [diakonos], used here of deacons) of all, just as the Son of Man came not to be served but to serve (διακονέω [diakoneō], as in 1 Tim 3:10, 13).
18 In the phrase the faith that is in Christ Jesus, the term faith seems to mean “what Christians believe, Christian truth,” rather than personal trust in Christ. So the whole phrase could mean that others will come to place greater confidence in them regarding Christian truth; but the word “confidence” is much more likely to refer to their own boldness to act on the truth of their convictions.

In other versions

For those who serve well as deacons gain a good standing for themselves and also great confidence in the faith that is in Christ Jesus.

Those who have served well gain an excellent standing and great assurance in their faith in Christ Jesus.

For those who have served well as deacons acquire a good standing for themselves and great boldness in the faith that is in Christ Jesus.

Those who do well as deacons will be rewarded with respect from others and will have increased confidence in their faith in Christ Jesus.

For those who have served well acquire a good standing for themselves, and great boldness in the faith that is in Christ Jesus.

For they that have used the office of a deacon well purchase to themselves a good degree, and great boldness in the faith which is in Christ Jesus.

Public Domain