As it is written - This is evidently a quotation made from Jeremiah 9:23-24. It is not made literally; but the apostle has “condensed” the sense of the prophet into a few words, and has retained essentially his idea.
He that glorieth - He that boasts or exults.
In the Lord - Not ascribing his salvation to human abilities, or learning, or rank, but entirely to God. And from this we see:
(1) That the design of the plan of salvation is to exalt God in view of the mind.
(2) That the design is to make us humble; and this is the design also of all his works no less than of the plan of salvation. All just views of the creation tend to produce true humility.
(3) It is an evidence of piety when we are thus disposed to exalt God, and to be humble. It shows that the heart is changed; and that we are truly disposed to honor him.
(4) We may rejoice in God. We have no strength, and no righteousness of which to boast; but we may rejoice in him. He is full of goodness and mercy. He is able to save us. He can redeem us out of the hand of all our enemies. And when we are conscious that we are poor, and feeble, and helpless; when oppressed with a sense of sin, we may rejoice in him as our God; and exult in him as our Saviour and Redeemer. True piety will delight to come and lay everything at his feet; and whatever may be our rank, or talent, or learning, we shall rejoice to come with the temper of the humblest child of poverty, and sorrow, and lack, and to say, “not unto us, not unto us, but unto thy name give glory for thy mercy, and for thy truth’s sake,” Psalms 115:1.
“Not to our names, thou only just and true,
Not to our worthless names is glory due;
Thy power and grace, thy truth and justice claim.
Immortal honours to thy sovereign name.”
Watts.