O God, who hast willed that the gate of mercy should stand open to the faithful: Look on us, and have mercy upon us, we beseech thee; that we who by thy grace are following the path of thy will may continue in the same all the days of our life; through Jesus Christ our Lord.
Can you be more specific with respect to its position within the Leonine sacramentary? I’m wondering: http://liberlocorumcommunium.blogspot.com/2015/03/ianua-misericordiae-tuae.html.
Nevermind. It’s no. 945 in the Gelasian (which is later than the “Leonine”/Veronese). My eye skipped over it because “misericordiae” comes before “ianuam” in that one (though after elsewhere). Interesting that the Companion to Common worship overlooks that, attributing it (without acknowledging its antiquity) to Bishop Kenneth Stevenson (1949-2011).
The key thing, though, is that I don’t think it occurs in the “Leonine”. The Old and 8th-century Gelasian and the much later Leofric (among others), but not the “Leonine” (Veronese).