This is the 3rd petition of the Lord's Prayer. The 1st is the address of "Our Father" and the foundation of our prayer. Then the petitions that are divided relating to God and His Kingdom and now we have the Will of God. We would expect some explanation or clarity on exactly what the will of God is but the catechism talks about OUR will putting its finger on the fact that we must always put OUR will UNDER and in submission ot the will of God!
How is the will of God related to our will? His will is His determined good pleasure. That which He determines for all things! He does His good pleasure...what He wants to do. (His attributes are His names and they never strive with one another.) That is His will! We too have a desire and determination though sometimes our desire outstrips our ability. Not so with God. And His will/council is ALWAYS good as it always fulfills HIS joy and desire. Your and my desire sometimes are NOT what they ought to be but NOT so with God! When we desire "Thy will be done" we know though details are obscure. ALL things in our life are controlled by the all comprehensive will of God. But we do not know the minute details....but in God revealing His will in broad outline form we can determine. God's secret that He reveals to us. God purposes in Christ to redeem unto Himself a Church! That is the will of God, the secret of God that is with us. Some things God makes very well known to us while particulars of His secret will we do not know.
That is why we pray that we submit and renounce our will to God's will! His plan may be completely different that what you and I will and desire. It is His will alone that is good and perfect however. Not ours because we are sinful men and women who let sin creep into our lives against the will of God and NOT in harmony with it! (Paul speaks about "our reasonable service" and "our calling to prove God's will") We have to ask what is our reasonable service?! The will of God is our sanctification that we are TRANSFORMED and crucify the old man rather than to be CONFORMED. That's what we pray for!
Then we understand why we pray "on earth as it is in heaven." The angels do not struggle with this. Ask yourself how would the angels handle it?! They continually sing praise to God! We stand in our station and calling we are in and do it as an angel would to it...TO THE WILL OF GOD! Do we think about how the angels in glory praise God? And when we see our will is different from the will of God we must submit our will unto His. Often we see things in our life go in a different direction than we want them to go, or what we pray for does not happen and our prayers change as His will is revealed to us and different from ours. (men like Paul pleaded with God....and men like Job were contect with God's will.) And our desires must be in conformity with His. He prayed "not my will but yours" in the garden and is exactly what you and I must do.