Ezekiel is a prophet during the exile. In chapters 16&17, he says that Israel was a little girl saved and chosen by God. But the adopted child grew up to be wayward. Then, using the image of marriage, Israel is graphically portrayed as unfaithful and wanton. She does not deserve to be rescued, but the merciful God, ever faithful to His covenant to Israel, saves her in His longsuffering love.
The tree in today's first reading is a metaphor. Israel's King is the top of the cedar, clipped off and transplanted to Babylon in the exile. This prophecy is God's promise of a new beginning. There will be a new king planted--like a majestic cedar stretching to the heights--and the Kingdom will be expansive. This messianic promise is fulfilled by Jesus on a tree--the cross. Crucified Kings disappoint the worldly. It takes the eyes of faith and a pure heart to see God in Jesus.
The "weakness" of God is called the scandal of the cross. It generates the parables today. Jesus compares the kingdom of God to seed growing in a field. Jesus want us to understand how God works--slowly and, often, unimpressively. Jesus ends the parable with a quote from the prophet Joel (3:13, see below). The verse is part of a prophecy where God condemns the nations and promises deliverance to Israel. Jesus turns this expectation on its head, announcing judgment on Israel as well, for failing to accept Him. NT Wright's insight (in "Mark For Everyone") is that the growing seed actually finds its fulfillment in the burial and resurrection of Jesus. The Kingdom will grow undetected among us. Jesus warns against being dismissive of the small beginnings of His ministry.
The second parable has a similar warning. People doubted that an itinerant preacher-healer could be ushering in God's great victory? So Jesus points to the tiny mustard seed and invites us to "see how God works." The humble seed becomes a bush which is then compared to the great tree of Zechariah in its size and scope. Jesus' parables are commentary on Scripture, let those who have ears to hear, hear.
Mark 4 should give us great consolation today. As we see hostility to Jesus growing, it is easy to be dismayed. We are becoming smaller, weaker and are increasingly marginalized. We read about people losing their livelihoods for the faith. It is shocking and can be disheartening.
Jesus says: Size is not the measure. Human power is not the means. His message is apocalyptic. God will establish His Kingdom among us. Our human effort can never build the kingdom. His message is ancient. Our work is to be open to receive purification. We are to pray, to learn, to trust and love. we are to guard our thoughts and offer our hearts to the Holy Spirit. Salvation is the hidden work of God in each heart. Purifying, healing, and sanctifying. This is how God saves the world. Like a mustard seed in each human heart. This is good news. We are a small, unimportant parish, but God is among us healing and saving. Our power can not achieve much, but the Holy Spirit quietly does great things. The purpose of life is theosis, seek union with your God and trust in Him.
Joel 3 "For behold, in those days and at that time, when I restore the fortunes of Judah and Jerusalem, I will gather all the nations and bring them down to the valley of Jehosh'aphat, and I will enter into judgment with them there, on account of my people and my heritage Israel, because they have scattered them among the nations, and have divided up my land, [directly addresses various nations and makes accusations]….
Proclaim this among the nations: Prepare war, stir up the mighty men. Let all the men of war draw near, let them come up. Beat your plowshares into swords, and your pruning hooks into spears; let the weak say, "I am a warrior." Hasten and come, all you nations round about, gather yourselves there. Bring down thy warriors, O Lord. Let the nations bestir themselves, and come up to the valley of Jehosh'aphat; for there I will sit to judge all the nations round about. Put in the sickle, for the harvest is ripe. Go in, tread, for the wine press is full. The vats overflow, for their wickedness is great. Multitudes, multitudes, in the valley of decision! For the day of the Lord is near in the valley of decision. The sun and the moon are darkened, and the stars withdraw their shining. [RSV]
Nebuchadnezzar had a dream of a similar large tree which shaded all. He was the tree but his power as king was, in fulfillment of the dream, taken from him for awhile before he was restored.
See a number of Biblical references to watching and waiting.