When speaking that God is merciful with us, it is being said that this of mercy is a kind gesture of God with all those who seek Him. The mercy of God is great for the whole world.
But if from there you seek the Lord your God, you will find him if you seek him with all your heart and with all your soul.
When we seek the Lord with all our heart and ask Him, He will not reject us because He is a God who does not reject or despise an afflicted heart. He is God, shows mercy to all His children.