Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Psa 138:1-5) The psalmist praises God for answering prayer.
(Psa 138:6-8) The Lord's dealing with the humble and the proud.
When we can praise God with our whole heart, we need not be unwilling for the whole world to witness our gratitude and joy in him. Those who rely on his loving-kindness and truth through Jesus Christ, will ever find him faithful to his word. If he spared not his own Son, how shall he not with him freely give us all things? If God gives us strength in our souls, to bear the burdens, resist the temptations, and to do the duties of an afflicted state, if he strengthens us to keep hold of himself by faith, and to wait with patience for the event, we are bound to be thankful.
Though the Lord is high, yet he has respect to every lowly, humbled sinner; but the proud and unbelieving will be banished far from his blissful presence. Divine consolations have enough in them to revive us, even when we walk in the midst of troubles. And God will save his own people that they may be revived by the Holy Spirit, the Giver of life and holiness. If we give to God the glory of his mercy, we may take to ourselves the comfort. This confidence will not do away, but quicken prayer. Whatever good there is in us, it is God works in us both to will and to do. The Lord will perfect the salvation of every true believer, and he will never forsake those whom he has created anew in Christ Jesus unto good works.