Why do elders vote
on new members ?
Yes, the elders vote to receive (or not receive) people as members of UPC. This is common practice among churches where the elders' responsibility to "watch over the flock" (1 Peter 5:2) and be "shepherds of the church of God" (Acts 20:28) are taken seriously.
Elders are charged by God with the care of the purity and peace of the church. One way we carry out our charge is to expect people joining our church to give a credible profession of faith in Christ. That's why elders meet with everyone who wants to join. In some churches (like the one I came here from), the entire elder board meets with each person or family and listens to their testimony. At UPC, we think that's a bit intimidating (!), so we meet with people one on one (or one elder to one family). However, after that meeting, the elder still reports to the entire elder board and there is a formal vote by the board. 99.9% of the time, this is a formality. The board of elders normally takes the recommendation of the elder who heard the person's testimony, and that's that. But it's still important that the elders collectively agree to receive each member. Hebrews 13:17 says that "they keep watch over you as those who must give an account."
I suppose such a process could be implemented in a harsh, judgmental way. But at UPC we seek to be gracious and gospel-centered as elders. All that is required for a person to join UPC is a credible profession of faith in Jesus Christ. Unless there is some evidence of stubborn ungodliness that calls into question the credibility of that person's testimony, we vote to receive him or her into communing membership. He or she may be just a beginner on the journey, or a small child, or someone with doubts and dysfunctions remaining...that's OK. The elders do not sit in judgment over such persons; rather, we acknowledge that God is at work in that person and he or she should be welcomed into the church family with open arms.
Now obviously, unbelievers are welcome at UPC too. We should love them, help them feel at home among us, and let them know they're among friends. This is how they can hear the gospel and see it lived out. But this does not mean they should become members of the church. If people are not questioned about their faith in Jesus, if we did not have some standards or expectations of the members, there would be no accountability, membership vows would be meaningless, and the vitality and doctrine of the church would be weakened. So at UPC (like most evangelical churches), we seek to obey God's charge to the elders while doing so in a gracious way.