Charles Spurgeon, The Metropolitan Tabernacle Pulpit Sermons (London: 1877), 23:642:
The more happy we can be in our God the more thoroughly will the will of Christ be fulfilled in us, for he desired that our joy might be full. The more you rejoice in God the more you will recommend true religion. The more full of delight you are, especially in trying times, the more you will glorify God. Few things are at the same time both pleasant and profitable, but holy joy and peace possess that double excellence. Fullness of spiritual joy is both the index and the means of spiritual strength.