But I am poor and needy - This is the same as in Psalm 40:17.
Make haste unto me, O God - Hebrew, אלהים 'Elohiym. In the parallel place in Psalm 40:17, this is, "The Lord thinketh upon me," - where the Hebrew word is not אלהים 'Elohiym, but אדני tub ,my 'Adonāy (Lord). The word "make haste" seems to have been introduced here by design - thus carrying out the main idea in Ps. 40, but turning here to "petition" what is there stated as a "fact."
Thou art my help and my deliverer - The close of the psalm is the same as the close of Ps. 40, except that the word Lord (Yahweh) is used here instead of "God" (אלהים 'Elohiym). It is not possible to ascertain whether these changes were mere matters of taste, or whether they were designed to adapt the psalm to some new circumstance, or to the special feelings of the psalmist at the time. There is no evidence that they are mere errors of transcribers, and indeed the changes are so made that this cannot be supposed. The change of the names אלהים 'Elohiym, יהוה Yahweh, and אדני 'Adonāy, for example, is such as must have been by design, and could not have been made by copyists. But what that design was must remain unknown. The alterations do not in any way, as far as we can understand, affect the sense.

But I am poor and needy - עני ואביון ani veebyon, I am a poor man, and a beggar - an afflicted beggar; a sense of my poverty causes me to beg.
Thou art my help - I know thou hast enough, and to spare; and therefore I come to thee.
Make no tarrying - My wants are many, my danger great, my time short. O God, delay not!

But I [am] (e) poor and needy: make haste unto me, O God: thou [art] my help and my deliverer; O LORD, make no tarrying.
(e) Because he had felt God's help before, he grounds on experience, and boldly seeks him for help.

But I am poor and needy,.... In Psalm 40:17 it follows, yet "the Lord thinketh on me"; instead of which it is here; see Gill on Psalm 40:17;
make haste unto me, O God; which repeats for sense the same petition as in Psalm 71:1;
thou art my help and my deliverer; O Lord, make no tarrying; in Psalm 40:17 it is, "O my God".