Berkhof:

e. The longsuffering of God. The longsuffering of God is still another aspect of His great goodness or love. The Hebrew uses the expression ’erek ’aph, which means literally “long of face,” and then also “slow to anger,” while the Greek expresses the same idea by the word makrothumia. It is that aspect of the goodness or love of God in virtue of which He bears with the froward and evil in spite of their long continued disobedience. In the exercise of this attribute the sinner is contemplated as continuing in sin, notwithstanding the admonitions and warnings that come to him. It reveals itself in the postponement of the merited judgment. Scripture speaks of it in Ex. 34:6; Ps. 86:15; Rom. 2:4; 9:22; I Pet. 3:20; II Pet. 3:15. A synonymous term of a slightly different connotation is the word “forbearance.”

Louis Berkhof, Systematic Theology, (Grand Rapids: Eerdmans, 1969), 72-73. [Underlining mine.]