How do we know that Jesus' prayer for protection is effective?

In His prayer, Jesus expressly asks the Father to protect His own from the evil one (John 17:15). This protection does not imply a removal from all trials or suffering but rather an assurance that despite such challenges, believers will be safeguarded from falling away from their faith. Just as Job was protected from losing faith during his trials, Jesus guarantees that His followers will not be abandoned. This reflects God's sovereignty and the efficacy of Christ's intercessory work, ensuring that all whom the Father has given Him will persevere in their faith and ultimately be saved.