Boyd’s Bible Dictionary:

(pity). Almsgiving enjoined by Mosaic law (Lev. 19:99And when ye reap the harvest of your land, thou shalt not wholly reap the corners of thy field, neither shalt thou gather the gleanings of thy harvest. (Leviticus 19:9); Ruth 2:22And Ruth the Moabitess said unto Naomi, Let me now go to the field, and glean ears of corn after him in whose sight I shall find grace. And she said unto her, Go, my daughter. (Ruth 2:2)). Every third year the tithes of increase were shared with the Levite, the stranger, the fatherless and widow (Deut. 14:2828At the end of three years thou shalt bring forth all the tithe of thine increase the same year, and shalt lay it up within thy gates: (Deuteronomy 14:28)). Receptacles for taking of alms placed in the Temple (Mark 12:4141And Jesus sat over against the treasury, and beheld how the people cast money into the treasury: and many that were rich cast in much. (Mark 12:41)). Almsgiving exhorted (Acts 11:3030Which also they did, and sent it to the elders by the hands of Barnabas and Saul. (Acts 11:30); Rom. 15:25-2725But now I go unto Jerusalem to minister unto the saints. 26For it hath pleased them of Macedonia and Achaia to make a certain contribution for the poor saints which are at Jerusalem. 27It hath pleased them verily; and their debtors they are. For if the Gentiles have been made partakers of their spiritual things, their duty is also to minister unto them in carnal things. (Romans 15:25‑27); 1 Cor. 16:1-41Now concerning the collection for the saints, as I have given order to the churches of Galatia, even so do ye. 2Upon the first day of the week let every one of you lay by him in store, as God hath prospered him, that there be no gatherings when I come. 3And when I come, whomsoever ye shall approve by your letters, them will I send to bring your liberality unto Jerusalem. 4And if it be meet that I go also, they shall go with me. (1 Corinthians 16:1‑4)).

Concise Bible Dictionary:

Offerings given to the poor. It was righteous to do so: hence, giving to the poor is called righteousness (Psa. 112:99He hath dispersed, he hath given to the poor; his righteousness endureth for ever; his horn shall be exalted with honor. (Psalm 112:9); 2 Cor. 9:99(As it is written, He hath dispersed abroad; he hath given to the poor: his righteousness remaineth for ever. (2 Corinthians 9:9)). In the law provision was made for the poor (Ex. 23:1111But the seventh year thou shalt let it rest and lie still; that the poor of thy people may eat: and what they leave the beasts of the field shall eat. In like manner thou shalt deal with thy vineyard, and with thy oliveyard. (Exodus 23:11); Lev. 19:1010And thou shalt not glean thy vineyard, neither shalt thou gather every grape of thy vineyard; thou shalt leave them for the poor and stranger: I am the Lord your God. (Leviticus 19:10)). It is declared that the poor would never cease out of the land; and if not relieved and they cried to the Lord, it would be accounted a sin against those who should have aided them (Deut. 15:7-117If there be among you a poor man of one of thy brethren within any of thy gates in thy land which the Lord thy God giveth thee, thou shalt not harden thine heart, nor shut thine hand from thy poor brother: 8But thou shalt open thine hand wide unto him, and shalt surely lend him sufficient for his need, in that which he wanteth. 9Beware that there be not a thought in thy wicked heart, saying, The seventh year, the year of release, is at hand; and thine eye be evil against thy poor brother, and thou givest him nought; and he cry unto the Lord against thee, and it be sin unto thee. 10Thou shalt surely give him, and thine heart shall not be grieved when thou givest unto him: because that for this thing the Lord thy God shall bless thee in all thy works, and in all that thou puttest thine hand unto. 11For the poor shall never cease out of the land: therefore I command thee, saying, Thou shalt open thine hand wide unto thy brother, to thy poor, and to thy needy, in thy land. (Deuteronomy 15:7‑11)). On the other hand, we read that “he that hath pity upon the poor lendeth to the Lord, and that which he hath given will he pay him again” (Prov. 19:1717He that hath pity upon the poor lendeth unto the Lord; and that which he hath given will he pay him again. (Proverbs 19:17)). In the New Testament the same thing is enforced. We are exhorted to do good unto all men, especially unto them of the household of faith (Gal. 6:1010As we have therefore opportunity, let us do good unto all men, especially unto them who are of the household of faith. (Galatians 6:10)). “He that soweth sparingly shall reap also sparingly....the Lord loveth a cheerful giver”; and whole chapters were written to stir up the saints to give liberally to the poor in Judaea. “It is more blessed to give than to receive.”

From Manners and Customs of the Bible:

Some have thought from these words that it was customary, literally, to sound a trumpet before an alms-giver. However this might have been in the streets, it certainly could not be permitted “in the synagogues,” as it would disturb the services there. There is no evidence whatever that any such custom was ever practiced by alms-givers. The words are therefore to be understood in a figurative sense, which is based on the custom of heralds making public announcements; or there may be an allusion to the trumpet which was sounded before actors and gladiators when they were brought into the theater; or to the trumpet which was sounded six times from the roof of the synagogue to usher in the Sabbath. We have corresponding phrases in modern languages. “In German, ausposaunen and an die grosse Glocke schlagen; in English, to sound one’s own trumpet, ‘to trumpet forth,’ every man his own trumpet; in French, faire quelque chose tambor battant, trompetter; in Italian, trompetar, bucinar” (Tholuck, Sermon on the Mount, p. 298). The idea of the text is simply that alms-giving should be unaccompanied by ostentation.
It was customary among the Jews to give alms to the poor who were assembled before the entrance to the temple or synagogue. This is referred to in Acts 3:33Who seeing Peter and John about to go into the temple asked an alms. (Acts 3:3), where the lame man asked alms of Peter and John as they were going into the temple. Chrysostom makes reference to the custom as afterward practiced in front of the early Christian churches. See Bingham, Antiquities of the Christian Church, book 13, chap. 8, § 14. It may be that in the text the word “streets” refers to the space in front of the synagogue.
In the synagogues there was a regular form of giving alms, the offerings being deposited in the alms-boxes before the prayers began. Thus the Saviour speaks first of alms-giving, and next of prayer. Sometimes, on special occasions, the congregation handed their alms to the proper officer.

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