Bible Questions and Answers

A visitor writes,

"Can you explained 1 Corinthians 1:18, and Matthew 28:19 these are the references of the catholics are they sign of the cross. What is sign of the Cross?"

1 Corinthians 1:18  For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God.
The message of the cross is the preaching that Jesus was crucified.
1 Corinthians 1:23  But we preach Christ crucified, unto the Jews a stumblingblock, and unto the Greeks foolishness;
Christians understand that Christ’s sacrifice was necessary to make atonement for our sins.
The Jews wouldn’t accept that their promised Messiah would be crucified despite it being clearly prophesied in Psalm 22. 
Psalms 22:16  For dogs have surrounded Me; The congregation of the wicked has enclosed Me. They pierced My hands and My feet;
The Greeks considered the Gospel of a crucified Messiah to be foolish.
There is no record of the Apostles making the ‘sign of the cross’ nor any instruction in the New Testament to make it.
From Wikipedia: https://en.wikipedia.org/wiki/Sign_of_the_cross
Making the sign of the cross (Latin: signum crucis), also known as blessing oneself or crossing oneself, is both a prayer and a ritual blessing made by members of some branches of Christianity. It is a very significant prayer because Christians are acknowledging their belief in the triune God, or the Holy Trinity: God the Father, God the Son and God the Holy Spirit. There are three variants of the sign of the cross, including a large sign of the cross made across the body, a small sign of the cross traced on the forehead or objects, as well as a lesser sign of the cross made over the forehead, lips and heart.
The use of the sign of the cross traces back to early Christianity, with the third-century treatise Apostolic Tradition directing that it be used during the minor exorcism of baptism, during ablutions before praying at fixed prayer times, and in times of temptation.
The large sign of the cross is made by the tracing of an upright cross or Greek cross across the body with the right hand, often accompanied by spoken or mental recitation of the Trinitarian formula: "In the name of the Father, and of the Son, and of the Holy Spirit. Amen. "The movement is the tracing of the shape of a cross in the air or on one's own body, echoing the traditional shape of the cross of the crucifixion of Jesus. Where this is done with fingers joined, there are two principal forms: one—three fingers (to represent the Trinity), right to left—is exclusively used by Christians who belong to the Eastern Orthodox Church, the Church of the East, Eastern Lutheran Churches and the Eastern Catholic Churches in the Byzantine and Syriac Christian traditions; the other—left to right to middle, other than three fingers—used by Christians who belong to the Latin Rite of the Catholic Church, Lutheranism, Anglicanism and Oriental Orthodoxy. The large sign of the cross is used in some denominations of Methodism and within some branches of Reformed Christianity.

The use of the small sign of the cross has been documented in early Christianity by Tertullian, an Ante-Nicene Church Father, who wrote in AD 204 in De Corona ('On Crowns'): "In all our actions, when we come in or go out, when we dress, when we wash, at our meals, before retiring to sleep we form on our foreheads the sign of the cross." Tertullian attested to the Christian practice of tracing this small sign of the cross on objects, such one's bed before sleeping. It is traced on the forehead, or objects, with the thumb (sometimes using holy water or anointing oil). The small sign of the cross is made on the forehead during the rites of baptism and the anointing of the sick in Catholicism, Lutheranism and Anglicanism. In the Baptist, Methodist, and Pentecostal traditions of Christianity, the small sign of the cross is often made on the forehead of the recipient during ordinations, anointing of the sick and deliverance prayers. Christians of various denominations have traced the small sign of the cross onto doors or windows of their dwellings as a house blessing. The small sign of the cross is additionally used during certain observances, such as during the imposition of ashes on Ash Wednesday, in which ashes are marked on the forehead of a believer using the small sign of the cross.
Origins
The small sign of the cross was originally made in some parts of the Christian world with the thumb of the right hand, being used on the forehead to bless oneself, along with being used to bless various objects, as attested by Tertullian, an Ante-Nicene Church Father. In other parts of the early Christian world it was done with the whole hand or with two fingers. Around the year 200 in Carthage (modern Tunisia, Africa), Tertullian wrote: "We Christians wear out our foreheads with the sign of the cross." He documented that Christians would trace the sign of the cross on their beds prior to sleeping. In the 4th century, the small sign of the cross was applied to various parts of the body. The 6th century saw the development of the large sign of the cross as a "four-point movement traced across the chest or in the air".
Hippolytus of Rome, in his Apostolic Tradition, recommends sealing oneself the forehead in times of temptation, with it being described as the "Sign of the Passion." Vestiges of this early variant of the practice remain: in the Masses of the Roman Rite in the Catholic Church, the Lutheran Churches and the Anglican Churches, the celebrant makes this gesture on the Gospel book and—together with the congregation—on his forehead, lips, and on his heart at the proclamation of the Gospel (known as the lesser sign of the cross); on Ash Wednesday the small sign of the cross is traced in ashes on the forehead; chrism is applied, among places on the body, on the forehead for the Holy Mystery of Chrismation in the Eastern Orthodox Church.
Large sign of the cross
Gesture
The actual motion of the large sign of the cross is heavily disputed, the Byzantine orthodox states the right to left motion to be the more ancient way whereas writings by Bar Salibi and other Syriac prose writers show that the left to right motion predates the right to left signage. Western Catholics (the Latin Church) have made the motion from left to right, while Eastern Catholics follow the traditional signage of right to left. This gesture was also used in Western Europe into the high Middle Ages.
In the Eastern Orthodox and Byzantine Catholic (Eastern Catholics) churches, the tips of the first three fingers (the thumb, index, and middle ones) are brought together, and the last two (the "ring" and little fingers) are pressed against the palm. The first three fingers express one's faith in the Trinity, while the remaining two fingers represent the two natures of Jesus, divine and human.
Motion
The large sign of the cross is made by touching the hand sequentially to the forehead, lower chest or stomach, and both shoulders, accompanied by the Trinitarian formula: at the forehead "In the name of the Father" (or In nomine Patris in Latin); at the stomach or heart "and of the Son" (et Filii); across the shoulders "and of the Holy Spirit/Ghost" (et Spiritus Sancti); and finally: "Amen".
There are several interpretations, according to Church Fathers: the forehead symbolizes Heaven; the solar plexus (or top of stomach), the earth; the shoulders, the place and sign of power. It also recalls both the Trinity and the Incarnation. Pope Innocent III (1198–1216) explained: "The sign of the cross is made with three fingers, because the signing is done together with the invocation of the Trinity. [...] This is how it is done: from above to below, and from the right to the left, because Christ descended from the heavens to the earth".
There are some variations: for example a person may first place the right hand in holy water. After moving the hand from one shoulder to the other, it may be returned to the top of the stomach. It may also be accompanied by the recitation of a prayer (e.g., the Jesus Prayer, or simply "Lord have mercy"). In some Catholic regions, like Spain, Italy and Latin America, it is customary to form a cross with the index finger and thumb and then to kiss one's thumb at the conclusion of the gesture.
Etc.

I hope this helps,
God bless.
Glenn