This is a person who intervenes and brings two estranged parties together in reconciliation.
God is holy and can’t look on sin, whereas sinful man’s best deeds are as filthy rags (Isa 64:6). It is only through Jesus Christ that we can approach God, as He is the mediator of the new covenant – He brokered a settlement on our behalf (1 Tim 2:5,6; Heb 9:15, 12:24). The blood of Christ is the means whereby our sins can be removed, so we are reconciled to God and have peace with Him (Rom 5:1,10,11; Eph 1:7). Christ’s mediation provides ongoing access to God, presenting our thanksgiving and praise to Him, making our spiritual sacrifices acceptable, and interceding for us (Jn 14:6; Col 3:17; Heb 7:25, 13:15; 1 Jn 2:1). We don’t need to (and in fact can’t) approach God through any other person or means, for Jesus is the only way to God (Act 4:12).