Question and answer 4 of the Westminster Shorter Catechism helpfully presents the biblical teaching on the Lord’s character, explaining that “God is a Spirit, infinite, eternal, and unchangeable, in his being, wisdom, power, holiness, justice, goodness, and truth.” This statement portrays His essential attributes, revealing that His other character traits flow from the aforementioned list. Mercy, for example, is one expression of His essential attribute of goodness. Properly speaking, mercy cannot be an essential attribute of God because then He would be obligated to show mercy, and obligated mercy is an oxymoron. The Lord cannot show mercy if He is not good, but He can still be good even if He never shows mercy. After all, when He gives people what they deserve, He does not compromise His goodness and justice (Rom. 9:14–18).
Consequently, we can never raise our fists to heaven and demand that God show us mercy because of who we are or what we have done. All we can do is humbly exercise faith — admit our sin, confess that we deserve only condemnation, ask for forgiveness and mercy, entrust ourselves to Jesus, and believe the promise of salvation. And the Lord always saves those who approach Him this way (Rom. 10:13).
Apart from the work of the Spirit, we always appeal to God’s justice for our standing with Him. This would not be a problem if people by nature accepted what they know is true — the Lord’s justice demands perfection (Lev. 18:4–5). If people could accept this on their own, they would see their depravity and abandon their appeal to His justice, approaching Him by faith alone, appealing to His mercy. But until the Spirit changes our hearts, we water down God’s justice, thinking that He accepts our “good works” even when done inconsistently or halfheartedly. This error is fatal, as all who seek redemption by their good works must finish what they start — they must keep the whole law flawlessly, an impossibility for sinners (Acts 15:10; Gal. 5:3).
People who trust in their works think they can boast in them, but all such bragging is futile. Yet those who understand that salvation is not of themselves or their works at all can boast properly (Eph. 2:9). They can boast of the great mercy of God that was poured out on them when they least deserved it and give the Lord all the glory for their salvation (2 Cor. 10:17; Gal. 6:12–14).