John Calvin Commentary 1 Timothy 3:10

"And let these also first be proved; then let them serve as deacons, if they be blameless." — 1 Timothy 3:10 (ASV)

And let those be first tried He wishes that those who are chosen should not be unknown, but that their integrity should be ascertained, like that of the bishops. And from this it is evident, that they are called blameless who are not stained by any marked vice. Besides, this trial is not for a single hour, but consists in long experience. In short, when deacons are to be ordained, the choice must not fall at random, and without selection, on anyone who comes to hand, but those men are to be chosen who are approved by their past life in such a manner that, after what may be called full inquiry, they are ascertained to be well qualified.