Psalm 138  Once again I turn to Matthew Henry's Commentary as I meditate on this psalm and once again I hear the Shepherd's voice bringing me comfort and mercy, resulting in praise and thanksgiving to His holy Name!   V. 6-8 detail 3 things that David is comforted by:
v6 - God favours the lowly, the humble.  He, who is transcendent, infinite, and self-contained, who has no need of anything from any of His creations, "smiles upon them as  well pleased with them" .   Not only that but He will honor them and lift them up.  But, those who are proud and boastful, He will reject and disown.   Here is the sum of the gospel,  " that penitent sinners shall be accepted of God, but the impenitent cast out;".
v7. - God cares for His afflicted, oppressed people.  " I walk in the midst of trouble" David says.  But he is encouraged by his hope in God's comfort, "Thou wilt revive me"; God's protection, " Thou wilt stretch forth Thy hand against the wrath of my enemies" ; and God's salvation, " And Thy right hand will save me" .   One hand stretches out against the enemy, and one hand reaches out to save us, His people.  " Christ is the right hand of The Lord, that shall save all those who serve Him." MHC.
v8 - God will complete the good work He has begun.  "The Lord will perfect that which concerns me" .  That which I need the most, He knows and He will do. "Every good man is most concerned about his duty to God and his happiness in God, that the former may be faithfully done and the latter effectually secured; and if indeed these are the things our hearts are most upon.... He that has begun it will perfect it."
David bases his confidence in these truths on the fact that the Lord's mercy, His lovingkindness, is everlasting.  " Our hopes that we shall persevere must be founded, not upon our own strength, for that will fail us, but upon the mercy of God, for that will not fail."  David makes this his prayer. " Do not forsake the works of Thy hand."   I am the work of His hands, even as David was.  If He forsakes me, I will fail. "Whatever good there is in us it is the work of God's own hands; he works in us both to will and to do; it will fail if He forsake it; but his glory, as Jehovah, a perfecting God, is so much concerned in the progress of it the the end that we main in faith pray, 'Lord do not forsake it'. Whom He love he loves to the end; and , as for God, his work is perfect."
Amen and Amen.