"The trees of the Lord are full of sap."—Psalm 104:16.
Without sap the tree cannot flourish or even exist. Vitality is essential to a Christian. There must be life—a vital principle infused into us by God the Holy Ghost, or we cannot be trees of the Lord. The mere name of being a Christian is but a dead thing, we must be filled with the spirit of divine life.
This life is mysterious. We do not understand the circulation of the sap, by what force it rises, and by what power it descends again. So the life within us is a sacred mystery. Regeneration is wrought by the Holy Ghost entering into man and becoming man's life; and this divine life in a believer afterwards feeds upon the flesh and blood of Christ and is thus sustained by divine food, but whence it cometh and whither it goeth who shall explain to us?
What a secret thing the sap is! The roots go searching through the soil with their little spongioles, but we cannot see them suck out the various gases, or transmute the mineral into the vegetable; this work is done down in the dark. Our root is Christ Jesus, and our life is hid in Him; this is the secret of the Lord. The radix of the Christian life is as secret as the life itself.
How permanently active is the sap in the cedar! In the Christian the divine life is always full of energy—not always in fruit-bearing, but in inward operations. The believer's graces, are not every one of them in constant motion? but his life never ceases to palpitate within. He is not always working for God, but his heart is always living upon Him.
As the sap manifests itself in producing the foliage and fruit of the tree, so with a truly healthy Christian, his grace is externally manifested in his walk and conversation. If you talk with him, he cannot help speaking about Jesus. If you notice his actions you will see that he has been with Jesus. He has so much sap within, that it must fill his conduct and conversation with life.