Part of the process of maturing is learning how to speak up for ourselves. Some have more difficulty with this than others. Those with shy or apprehensive personalities will suffer until they adjust and learn to speak up for themselves.
So we learn, but then we recognize that sometimes it might be better to have someone else speak up for us. There may be a benefit in having another speak on our behalf; not because we lack the courage, but simply because and advocate might be more effective.
This is a lesson that the book of Philemon teaches us. Onesimus is a runaway slave who asks Paul to speak to his owner, Philemon, about receiving him upon his return. 1st Century Roman law allowed for a runaway slave to appeal to a contemporary of his owner to speak on his behalf.
Where would we be if all we had was our own voice? Sometimes our help comes from the voices of others, people praying for us when we are too injured to pray for ourselves. Consider Jesus speaking on our behalf to the Father when our sin could never be justified by our own voices. Paul speaks on behalf of Onesimus and Jesus speaks on our behalf. Thanks be to God that we have learned to speak up for ourselves, but even more that we have an advocate in Jesus, who speaks up for us.