The Lord is gracious - See Psalms 86:5, note; Psalms 86:15, note.
And full of compassion - Kind; compassionate; ready to do good. See the notes at Psalms 103:8.
Slow to anger - See Psalms 103:8, where the same expression occurs.
And of great mercy - Margin, great in mercy. His greatness is shown in his mercy; and the manifestation of that mercy is great: great, as on a large scale; great, as manifested toward great sinners; great, in the sacrifice made that it may be displayed; great, in the completeness with which sin is pardoned - pardoned so as to be remembered no more.