The answer
Drawing the sign of the cross three times over the tunic, the priest blesses it to protect the deacon against the devil's temptations during the Divine Liturgy. The priest's responsibility is to make sure that the deacons are well prepared to participate in the Divine Liturgy service. That is to say: they are members of the Church, observing the fast, if it is a fasting period; and that there is no obstacle preventing them from serving and partaking of the Holy Eucharist.It is very inappropriate for a deacon wearing the Service tunic to go out of the church during the Divine Liturgy. Sadly enough, some deacons, especially the very young ones, create excuses to go out to the restroom or even just to have a break.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)