As to your question about praying for others, and the experience or gain which we derive from doing so, even though our prayers are not answered immediately:—
In the first place, praying for others can only happily follow in a heart at rest about itself, and knowing in itself the value of the desires which it expresses for another. It could not be true or happy in praying otherwise. Secondly, if I am praying for another, according to the will of God, and in current with the Spirit, I must receive from association, fellowship with the Spirit, the effect and influence of His society. It is not whether my prayer is successful, I have been in company with the Spirit of Christ in the prayer, and my own soul invigorated by the very passage of His thought through my mind. I cannot have His desire for another awakened in me, but by His Spirit, and elaborated there, I am sensible, on account of it, of the strength and bliss which below, to Him whose thought and desire is passing through my heart and mind; and this true spiritual desire will be accomplished according to God-that is, according to His mind, not after man’s judgment. Therefore, when a simple spiritual desire is awakened, and occupies your heart touching any of His people, you are not only invigorated by the stream of divine thought passing through you, but you may rest assured that God will effectuate it in some way, but in a way manifestly of Himself.
I am always thankful when I remember any, as I believe, and feel my Lord thinks of them: (what good is anything else?) may we abound therein; we should, if the Lord be our strength, and the armor is on! (Eph. 6)