Luke 18:8

“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 4:17-18; Revelation 11:1-13). 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.