Luke 18:8

“I say to you, that he will avenge them speedily.”

This could mean that when it finally comes it will come with speed, it will occur suddenly, unexpectedly and without delay. And then all will be put right. And as He then makes clear, this refers to the Second Coming. Alternatively it could mean ‘soon'. But in that case it is to be seen as ‘soon' from God's perspective. Delay will occur no longer than is necessary. (See 2 Peter 3:8).

In local situations deliverance may occur almost at once, and certainly after not too long a time, but overall it will occur in God's time. Things will never get out of hand. The second part of the verse might be seen as favouring speed of fulfilment when the time comes. Once the time does come for God to act nothing will delay its accomplishment. It will be swift and sure. Thus He makes clear that all for which we pray should be prayed for, and seen, in the light of that Day. Our main thoughts in praying should therefore be set on things above, and on the fulfilment of His purposes, as in the Lord's prayer. And as we pray we can then be absolutely confident that it will come about. But why then pray? It is not in order to change God's mind about things. It is to be because we are cooperating with God in the family business, and because we are often applying the general to our local situation. It is in order that we might remember that God is in it with us, and so that we might recognise and acknowledge continually our dependence on Him.

“Nevertheless, when the Son of man comes, will he find faith on the earth?”

And then comes the challenge, the open question, that in one way or another regularly comes at the end of what Jesus has to say. And that question is as to whether when the end comes, and Jesus comes in His glory, He will find persevering faith on earth. Whether He will find persistent and continuing prayer. It is a challenge to His listeners. It is not said, however, in order to instil doubt, but in order to encourage persistence in prayer in the face of whatever comes on them. Elsewhere it is made perfectly plain that in the last days there will be faith on earth (e.g. 1 Thessalonians 4:17; Revelation 11:1). There will be many who, like the skin-diseased Samaritan who was healed, will persistently return to give glory and thanksgiving to God. And this will be so in spite of any tribulation that they might face. This is especially exemplified in the Book of Revelation where the most dreadful events are intermingled with the thought of the endurance of God's true people.

Alternately ‘ten pistin' (thus with the article) could signify ‘those who are trusting', so placing more emphasis on the believing people rather than their faith, or it could signify ‘the faith', indicating what had been taught and is believed.