This short piece by Rutherford is perhaps the best concise explanation of how the Sacraments work. Rutherford gives the standard, widely prevalent, vanilla reformed view of the Reformation. The Sacraments work:
(1) as signs,
(2) as seals,
(3) are instruments by which faith works, and
(4) they are means of grace to be used in obedience to Christ’s command.
What is noteworthy about these distinctions is that one could not fully explain the sacraments without all four distinctions (these distinctions are necessary). Nor does one need more distinctions than these four in order to explain the Biblical material (these distinctions are sufficient to account for all of the Biblical data). Thus, one may rest assuredly that here is the Biblical view of how the Sacraments are means of grace. May it stir us up to greater faith in our Savior as we see Him represented and sealed to us in baptism and the Lord’s Supper!
Rutherford, Samuel – The Efficacy of the Sacraments 1644, 5 pages, being pp. 211-215 of his Due Right of Presbyteries