This was not something totally new, however. If anything, Jesus was passing onto his disciples the form of prayer characteristic of the psalms. There, too, we see prayers made with faith. Take Ps 13 as an example. It begins with a rather bleak description of the psalmist's conditions:
How long, O LORD? Will you forget me forever?
How long will you hide your face from me?
How long must I bear pain in my soul,
and have sorrow in my heart all day long?
How long shall my enemy be exalted over me?
The psalmist tells us that he has been forgotten by God—a miserable state of affairs, indeed. Moreover, this has been a reality for longer than the psalmist can withstand. His prayer is desperate and exhausted: how long, Lord? The stakes are high and the psalmist considers himself near death:
Consider and answer me, O LORD my God!
Give light to my eyes, or I will sleep the sleep of death,
and my enemy will say "I have prevailed";
my foes will rejoice because I am shaken.
In light of this, there seems no other plausible way to interpret the final verses except as a prayer with faith:
But I trusted in your steadfast love;
my heart shall rejoice in your salvation.
I will sing to the LORD,
because he has dealt bountifully with me.
None of this is yet a reality for the psalmist, but he speaks as if it is. This is therefore a prayer with faith. It is an interpretive act that interprets one's circumstances and futures through the prism of one's trust in and relationship with God. The prayer of faith says, This is the way the world will be, because I trust in God and he cares for me. So the psalmist prays and expects that God will save him from his troubles, because he trusts in God's hesed, his steadfast love.
So Christ teaches us to pray with faith, and this is not an invention of his. Rather, it is an eminently scriptural mode of prayer that draws from the practices of God's people stretching far back into antiquity.