Mat 7:13 Enter ye in at the strait gate: for wide is the gate, and broad is the way, that leadeth to destruction, and many there be which go in thereat:
Mat 7:14 Because strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it.
Mat 13:22 He also that received seed among the thorns is he that heareth the word; and the care of this world, and the deceitfulness of riches, choke the word, and he becometh unfruitful.
Mat 13:23 But he that received seed into the good ground is he that heareth the word, and understandeth it; which also beareth fruit, and bringeth forth, some an hundredfold, some sixty, some thirty.
Mat 13:14 And in them is fulfilled the prophecy of Esaias, which saith, By hearing ye shall hear, and shall not understand; and seeing ye shall see, and shall not perceive:
Mat 13:15 For this people's heart is waxed gross, and their ears are dull of hearing, and their eyes they have closed; lest at any time they should see with their eyes and hear with their ears, and should understand with their heart, and should be converted, and I should heal them.
Mat 13:16 But blessed are your eyes, for they see: and your ears, for they hear.
Mat 13:17 For verily I say unto you, That many prophets and righteous men have desired to see those things which ye see, and have not seen them; and to hear those things which ye hear, and have not heard them.
Mark 8:17 And when Jesus knew it, he saith unto them, Why reason ye, because ye have no bread? perceive ye not yet, neither understand? have ye your heart yet hardened?
Mark 8:18 Having eyes, see ye not? and having ears, hear ye not? and do ye not remember?
Luke 8:10 And he said, Unto you it is given to know the mysteries of the kingdom of God: but to others in parables; that seeing they might not see, and hearing they might not understand.
Luke 24:45 Then opened he their understanding, that they might understand the scriptures,
John 8:43 Why do ye not understand my speech? even because ye cannot hear my word.
John 8:44 Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it.
This is not to imply we should not pray or fulfill the commission; we should. It is commanded. The power of God and His promise in regards to bringing His sheep to Himself is our hope, our confidence. In this, frustration is alleviated.