In his book, Heaven on Earth, Thomas Brooks (1608-1680) writes all about assurance of salvation – it is essentially a treatise on that great subject. There Brooks deals with such things as proving that believers may attain a well-grounded assurance, pointing out what means may be used in order to obtain assurance, giving reasons why believers may lack assurance, and demonstrating the differences between true and counterfeit assurance. It is a very helpful and encouraging book.
There he also shows us the vital connection between the Lord’s Supper and assurance. He writes,
It was the principal end of Christ’s institution of the sacrament of the supper that he might assure them of his love, and that he might seal up to them the forgiveness of their sins, the acceptation of their persons, and the salvation of their souls, Mat. 26.27,28. The nature of a seal is to make things sure and firm among men; so the supper of the Lord is Christ’s broad seal; it is Christ’s privy-seal, whereby he seals and assures his people that they are happy here, that they shall be more happy hereafter, that they are everlastingly beloved of God, that his heart is set upon them, that their names are written in the book of life, that there is laid up for them a crown of righteousness, and that nothing shall be able to separate them from him who is their light, their life, their crown, their all in all. (p.27)
Brooks would have us to understand that the sacrament of the Lord’s Supper is primarily about assurance. It is “the principal end” (or main purpose) for which the Lord Jesus Christ instituted it for His people. The Supper is meant to reassure believers of Christ’s great love for them. It is, to use Brook’s words above, to “seal up to them the forgiveness of their sins, the acceptation of their persons, and the salvation of their souls.” A “seal” is given for the express purpose of assurance. It is “to make things sure and form among men.”
The Lord’s Supper is certainly not the only means whereby believers may attain, maintain, and be strengthened in their assurance of salvation, but it is certainly one of the most important, and one which must not be neglected. The very fact that the Lord Jesus instituted this Sacrament to be perpetually celebrated by His church until He returns (1 Corinthians 11:26) shows us our perpetual need for assurance. It also shows us how greatly our faithful Savior desires that His beloved people would have assurance of His great love for them.