Forgiven, Really?

As Christians God has forgiven our sins, right? God has completely and truly forgiven you.

Micah 7:19
You will again have compassion on us; you will tread our sins underfoot and hurl all our iniquities into the depths of the sea.

God has thrown our iniquities into the sea! The sea is miles and miles deep in some places. If God has completely forgiven us, why do we continually punish ourselves for short-comings that God has already forgotten about? I believe we fall short of the very position God has intended us to be raised up to, because we mull sins of the past, that are already forgiven, over and over in our heads until depression and a feeling of unworthiness sets in. We think that if we say the right things, help the right people, and even start to right programs and ministries that we can somehow earn the gift of salvation that God has already given to us freely. All we have to do is repent and believe.

Isaiah 55:7
Let the wicked forsake his way, And the evil man his thoughts. Let him turn to the Lord, and he will have mercy on him, and to our God, for he will freely pardon.

Ephesians 2:8-9
For it is by grace you (believers) have been saved, through faith - and this not from yourselves, it is the gift of God - not by works, so that no-one can boast.