On Psalm 25

In the night in which he was betrayed, the Lord said "Watch ye and pray, lest ye enter into temptation. The spirit truly is ready, but the flesh is weak" (Mk 14:38). Because the flesh is weak, believers should always watch and pray. A possible prayer is given in Ps 25.

(Ps 25:1) Unto thee, O LORD, do I lift up my soul.
(Ps 25:2) O my God, I trust in thee: let me not be ashamed, let not mine enemies triumph over me.
(Ps 25:3) Yea, let none that wait on thee be ashamed: let them be ashamed which transgress without cause.

A literal translation of the words for "transgress without cause" would be "act treacherously vainly". If the consequences of sin are considered, all who act treacherously act in vain. However, this is not always seen right away. Eventually it will be seen that everyone who has waited on the Lord was right to wait for him, and everyone who has acted treacherously, has acted in vain. So the latter, not the former, will be ashamed.

(Ps 25:4) Shew me thy ways, O LORD; teach me thy paths.
(Ps 25:5) Lead me in thy truth, and teach me: for thou art the God of my salvation; on thee do I wait all the day.
(Ps 25:6) Remember, O LORD, thy tender mercies and thy lovingkindnesses; for they have been ever of old.
(Ps 25:7) Remember not the sins of my youth, nor my transgressions: according to thy mercy remember thou me for thy goodness' sake, O LORD.

God knows all things, so he cannot forget anything. A prayer asking God to remember something is actually requesting God to consider that thing in his decisions. Verses 6 and 7 ask God to act in accordance with his compassion and kindness and not according to past sins and transgressions.

(Ps 25:8) Good and upright is the LORD: therefore will he teach sinners in the way.
(Ps 25:9) The meek will he guide in judgment: and the meek will he teach his way.

The word translated "meek" means also "humble". One is not really humble if he has not humbled himself before the Word of God.

(Ps 25:10) All the paths of the LORD are mercy and truth unto such as keep his covenant and his testimonies.
(Ps 25:11) For thy name's sake, O LORD, pardon mine iniquity; for it is great.
(Ps 25:12) What man is he that feareth the LORD? him shall he teach in the way that he shall choose.

Thus, a man who truly fears the Lord allows the Lord to choose the way of his life.

(Ps 25:13) His soul shall dwell at ease; and his seed shall inherit the earth.

Literally, the words for "at ease" are "in good". In the statement "his seed shall inherit the earth", "seed" refers to saved people. Indeed, such people will inherit the earth, as mentioned in passages such as Mt 5:5 and Ps 37:9. Thus, Ps 25:13 is a promise that his descendants will include saved people. The promise is not that every descendant will be saved. This could be seen by considering that not all descendants of Abraham have been saved (Mt 11:20-24, Lk 16:23-25, Ro 9:6-8).

(Ps 25:14) The secret of the LORD is with them that fear him; and he will shew them his covenant.

The word translated "secret" means also "counsel".

(Ps 25:15) Mine eyes are ever toward the LORD; for he shall pluck my feet out of the net.
(Ps 25:16) Turn thee unto me, and have mercy upon me; for I am desolate and afflicted.
(Ps 25:17) The troubles of my heart are enlarged: O bring thou me out of my distresses.
(Ps 25:18) Look upon mine affliction and my pain; and forgive all my sins.
(Ps 25:19) Consider mine enemies; for they are many; and they hate me with cruel hatred.
(Ps 25:20) O keep my soul, and deliver me: let me not be ashamed; for I put my trust in thee.
(Ps 25:21) Let integrity and uprightness preserve me; for I wait on thee.
(Ps 25:22) Redeem Israel, O God, out of all his troubles.

In verse 20, "I put my trust in thee" is stated in support of the petition "let me not be ashamed". We can infer that those who put their trust in the Lord will not be ashamed. This truth is stated explicitly in other passages, such as in Ro 10:11.

(Ro 10:11) For the scripture saith, Whosoever believeth on him shall not be ashamed.