"Let us therefore come boldly unto the throne of grace, that we may obtain mercy, and find grace to help in time of need" (Hebrews 4:16).
Grace grants to us the lavish favor deserved by the Lord Jesus Christ because of His perfect fulfillment of God the Father's will. Mercy withholds from us rightful judgment for our sins because our Savior bore it on our behalf.
We need both. We cannot independently merit God's favor because our sins disqualify us from such blessing. We are rather graciously "accepted in the Beloved" when we trust in the Beloved (Ephesians 1:6). Every "good gift and every perfect gift" we will ever receive comes to us not by our own merits, but rather by those purchased for us through the high cost of our Savior's suffering, forsakenness and death (James 1:17). Indeed, our next breath comes to us through the price of Blood, and a long eternity will grace us over and over again with with innumerable gifts obtained for us by immeasurable suffering.
"He hath not dealt with us after our sins; nor rewarded us according to our iniquities" (Psalm 103:10). The Lord Jesus also made a way for mercy to surround those who trust in His atoning sacrifice. "He that trusteth in the LORD, mercy shall compass Him about" (Psalm 32:10). Believers still sin, including the most devout among us (I John 1:8). Were it not for the mercy of the Savior, our salvation could no more be maintained than it could have been obtained. The Lord Jesus "ever liveth to make intercession for us," making possible ongoing forgiveness, cleansing and uninterrupted fellowship with our Heavenly Father despite times of unbelief and disobedience (Hebrews 7:25). He "delighteth in mercy," and the truth of the matter is that God desires to forgive and cleanse His trusting children far more than we desire to be forgiven and cleansed (Micah 7:25).
One day we shall be perfected in the direct presence of our Lord. We shall not need grace and mercy in the same way it is presently required. Nevertheless, we shall know with far greater understanding that every blessing of eternity comes to us because and only because our Savior made possible the abundant bestowal of God's goodness and the merciful avoidance of His wrath. We shall love the Lord Jesus then even more than we do now, joining the heavenly throng that falls before Him in wonder and rapture...
"And I beheld, and I heard the voice of many angels round about the throne and the beasts and the elders: and the number of them was ten thousand times ten thousand, and thousands of thousands; saying with a loud voice, Worthy is the Lamb that was slain to receive power, and riches, and wisdom, and strength, and honor, and glory, and blessing. And every creature which is in heaven, and on the earth, and under the earth, and such as are in the sea, and all that are in them, heard I saying, Blessing, and honor, and glory, and power, be unto Him that sitteth upon the throne, and unto the Lamb for ever and ever. And the four beasts said, Amen. And the four and twenty elders fell down and worshipped him that liveth for ever and ever."