Concise Bible Dictionary:


From Anstey’s Doctrinal Definitions:

Mercy is “not getting what we deserve”—i.e. being judged for our sins. It is often mentioned in contrast to grace, which has to do with “getting something we don’t deserve”—i.e. salvation and the many blessings associated with it. Thus, God extends His “mercy” to men in their sins (Eph. 2:44But God, who is rich in mercy, for his great love wherewith he loved us, (Ephesians 2:4)) because He does not want any to perish in a lost eternity (2 Peter 3:99The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance. (2 Peter 3:9)).
On the other hand, the "mercies" of God have to do with temporal things that God grants to men providentially in the vicissitudes of life on earth (Gen. 32:1010I am not worthy of the least of all the mercies, and of all the truth, which thou hast showed unto thy servant; for with my staff I passed over this Jordan; and now I am become two bands. (Genesis 32:10); Psa. 40:1111Withhold not thou thy tender mercies from me, O Lord: let thy lovingkindness and thy truth continually preserve me. (Psalm 40:11); Lam. 3:2222It is of the Lord's mercies that we are not consumed, because his compassions fail not. (Lamentations 3:22); 2 Cor. 1:33Blessed be God, even the Father of our Lord Jesus Christ, the Father of mercies, and the God of all comfort; (2 Corinthians 1:3); Phil. 2:11If there be therefore any consolation in Christ, if any comfort of love, if any fellowship of the Spirit, if any bowels and mercies, (Philippians 2:1); Col. 3:1212Put on therefore, as the elect of God, holy and beloved, bowels of mercies, kindness, humbleness of mind, meekness, longsuffering; (Colossians 3:12)). This would be things having to do with His care for people amidst the dangers of life, etc. Thus, in contrast to our blessings which are heavenly, spiritual, and eternal, the mercies of God are earthly and temporal provisions that He grants to men on earth. This distinction between mercy and mercies is a general thing in Scripture; there may be exceptions. (“Mercies” in Romans 12:11I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. (Romans 12:1) should be translated “compassions”).
The following quote from The Christian Friend magazine (E. Dennett, editor) is helpful in this regard: "In verse 3 [of Ephesians 1] we find the best kind of blessings, in the best place; they are in Christ, and they are all there. We have temporal mercies assuredly, but that is just a kind of passing thing, and not our portion" (The Christian Friend, vol. 9, 1882, pp. 213-214).