Shaking hands signified unity of purpose (2 Kings 10:15) and spiritual guidance was bound on fingers (Prov 7:3). A finger sprinkled the sacrificial blood upon the horns of the altar of the Tabernacle and the priests received blood upon the thumbs of their right hands (Exod 29:12, 20).
A rare dominant hereditary trait is the possession of extra fingers and toes, such as of the man of great stature at Gath (1 Chron 20:6).
Rehoboam stressed the burden of his yoke upon his people by following the advice of his young men to say, “My little finger is thicker than my father’s loins” (1 Kings 12:10). Jesus complained that the scribes and Pharisees laid burdens on men’s shoulders, but they themselves would not move them with their fingers (Matt 23:4).
The finger of God was like the hand of God, only His creative skill is suggested in such statements as “when I look at thy heavens, the work of thy fingers” (Ps 8:3). With it He wrote the Ten Commandments on tablets of stone (Exod 31:18). In a miracle He made the fingers of a man’s hand to appear and write on the plaster on the wall to pronounce doom on Belshazzar (Dan 5:5). Apparently the writing by Jesus on the ground in the presence of the accusers of the adulterous woman was a sentence of conviction (John 8:6, fn). Jesus said it was by the finger of God that He cast out demons, and Luke, a physician whose fingers would so often be used in healing, is the one who records this (Luke 11:20).
Not only did Jesus ask Thomas to test His reality by thrusting his finger into His side (John 20:27) but He blessed with His fingers when He healed the deaf man, and when “children were brought to him that he might lay his hands on them and pray” (Matt 19:13).
Lifting and laying on of hands for blessing was common. The position of the fingers was important in the early western church. Three upraised fingers stood for the Trinity, while the remaining two closed fingers signified the two natures of Christ.
International Standard Bible Encyclopedia (1915)
The fingers are to the Oriental essential in conversation; their language is frequently very eloquent and expressive. They often show what the mouth does not dare to utter, especially grave insult and scorn. The scandalous person is thus described in Pr 6:13 as "teaching" or "making signs with his fingers." Such insulting gestures (compare e.g. the gesture of Shimei in throwing dust or stones at David, 2Sa 16:6) are even now not infrequent in Palestine. The same habit is alluded to in Isa 58:9 by the expression, "putting forth of fingers. "
The fingers were decorated with rings of precious metal, which, with other jewelry worn ostentatiously on the body, often formed the only possession of the wearer, and were therefore carefully guarded. In the same way the law of Yahweh was to be kept: "Bind them (my commandments) upon thy fingers; write them upon the tablet of thy heart" (Pr 7:3).
Figurative: In 1Ki 12:10 and 2Ch 10:10 Rehoboam gives the remarkable answer to his dissatisfied people, which is, at the same time, an excellent example of the use of figurative language in the Orient: "My little finger is thicker than my father’s loins," a figure explained in the next verse: "Whereas my father did lade you with a heavy yoke, I will add to your yoke: my father chastised you with whips, but I will chastise you with scorpions." The Hebrew word used here for little finger is qoTen, literally, "pettiness," "unimportant thing."
The "finger of God," like the "hand of God," is synonymous with power, omnipotence, sometimes with the additional meaning of the infallible evidence of Divine authorship visible in all His works (Ps 8:3; Lu 11:20), especially in His law (Ex 8:19; 31:18; De 9:10; compare Ex 32:15,16).
The finger or digit as a linear measure is mentioned in Jer 52:21 (Greek daktulos; Josephus, Ant, VIII, iii, 4). It is equal to one finger-breadth, 1/4 of a hand-breadth (palm) = 18,6 millimeters or .73 inches.
The smallest of the Hebrew linear measures. It was equal to the breadth of the finger, or about 3/4 inches, four of which made a palm (Jer 52:21).
See Weights and Measures.