Catholics "know Him" through the Sacrament of Reconciliation.
In John 20:21 - before He grants them the authority to forgive sins, Jesus says to the apostles, "as the Father sent me, so I send you." As Christ was sent by the Father to forgive sins, so Christ sends the apostles and their successors forgive sins.
In John 20:22 - the Lord "breathes" on the apostles, and then gives them the power to forgive and retain sins. The only other moment in Scripture where God breathes on man is in Gen. 2:7, when the Lord "breathes" divine life into man. When this happens, a significant transformation takes place.
In John 20:23 - Jesus says, "If you forgive the sins of any, they are forgiven. If you retain the sins of any, they are retained." In order for the apostles to exercise this gift of forgiving sins, the penitents must orally confess their sins to them because the apostles are not mind readers. The text makes this very clear.
In Luke 5:24 - Luke also points out that Jesus' authority to forgive sins is as a man, not God. The Gospel writers record this to convince us that God has given this authority to men. This authority has been transferred from Christ to the apostles and their successors.
In 2 Cor. 5:18 - the ministry of reconciliation was given to the ambassadors of the Church. This ministry of reconciliation refers to the sacrament of reconciliation, also called the sacrament of confession or penance.
James clearly teaches us that we must “confess our sins to one another,” not just privately to God. James 5:16 must be read in the context of James 5:14-15, which is referring to the healing power (both physical and spiritual) of the priests of the Church. Hence, when James says “therefore” in verse 16, he must be referring to the men he was writing about in verses 14 and 15 – these men are the ordained priests of the Church, to whom we must confess our sins.
Acts 19:18 - many came to orally confess sins and divulge their sinful practices. Oral confession was the practice of the early Church just as it is today.
Christ is the only mediator (1 Tim. 2:5), but He was free to decide how His mediation would be applied to us. The Lord chose to use priests of God to carry out His work of forgiveness.
James clearly teaches us that we must “confess our sins to one another,” not just privately to God. James 5:16 must be read in the context of James 5:14-15, which is referring to the healing power (both physical and spiritual) of the priests of the Church. Hence, when James says “therefore” in verse 16, he must be referring to the men he was writing about in verses 14 and 15 – these men are the ordained priests of the Church, to whom we must confess our sins.
This command continued, as evidenced by the early Church Fathers. For example:
“In church confess your sins, and do not come to your prayer with a guilt conscience. Such is the Way of Life...On the Lord's own day, assemble in common to break bread and offer thanks; but first confess your sins, so that your sacrifice may be pure." Didache, 4:14,14:1 (c. A.D. 90).