Rashi on Exodus 34:6/רש"י על שמות ל״ד:ו׳

1ה׳ ה׳ THE LORD, THE LORD — This is the attribute of Divine mercy. The one (the first ה׳) alludes to God having mercy on the sinner before he sins and the other after he has sinned and repented (Rosh Hashanah 17b).

2אל GOD — This is also an attribute of Divine mercy (it is not, as אלהים, an attribute of stern justice). Thus also does Scripture say, (Psalms 22:2) “My God, my God (אלי ,אלי) why hast Thou forsaken me?” — for surely one would not say to the attribute of stern Justice “why hast Thou forsaken me?”! Thus have I found in the Mechilta d'Rabbi Yishmael 15:2:2.

3ארך אפים SLOW TO ANGER — He defers (מאריך) His anger and does not hasten to punish — it may be that the sinner will repent.

4ורב חסד AND ABUNDANT IN MERCY — to those who need mercy because they have not sufficient merits to be saved by them.

5ואמת AND TRUTH — faithfully rewarding those who perform His will.