Halakhah zu Tehillim 121:76

It is from the root of the commandment that he take his distancing from people as an example for his soul. As a person is distanced from all good as a result of sin, in order that he will repent from his evil way. And this is [the meaning] of their, may their memory be blessed saying (Arakhin 16b), "With evil speech, he separated a man from his wife and a man from his fellow. And therefore his tent is outside of the camp." And therefore it is fitting that he should call to every man that they veer away from him. And the general principle in all things is "With the measure that a man measures, [so] will he be measured" (Sotah 8b). And many do not know the understanding of this thing. As they think to explain this thing with God, may He be blessed, modeled on the recompense of men - that each one will recompense his fellow according to the good that he did by him, or according to the bad [that he did]. But the matter is not like this with God, blessed be He, - God forbid. As there is always only kindness and mercy with God, blessed be He; and His goodness is ready at every instant and every hour for all who are fitting to receive it. And 'the Guardian of Israel does not slumber and does not sleep.' [Rather] the intention of that which they, may their memory be blessed said about Him, blessed be He, "With the measure that a man measures, [so] will he be measured," is to say that according to the action of a man - whether for the good or the opposite - will he be set to receive recompense. As always in the same manner that a person sets his thoughts and does his actions - in that exact mold - will blessing or its opposite be drawn to him.

Ramban, may his memory be blessed, also wrote that when the father gives the money to the priest he should first give the child into the priest's hand, and the priest should say, "Which is more beloved to you, your son or these five sela?" And the father responds, "My son is more beloved to me." The priest immediately takes the silver coins and passes them over the head of the son and says, "This is in the place of this, traded for this, this is rendered no longer sacred through this. This goes out to the priest and this child should come to life and Torah and fear of heaven. May it be His will that as this one came to redemption, may he also come to Torah, marriage and good deeds, and let us say amen." The priest places his hands on the son's head and blesses him, according to how he knows to bless him, such as "May the Lord guard you, etc." (Psalms 121:5), or "As length of days and years of life, etc." (Proverbs 3:2) or "The Lord shall protect you from all evil and guard your soul, etc." (Psalms 121:7). And [the father] takes him out for all of his will. [This] and the rest of its details are elucidated in Tractate Bekhorot (see Tur, Yoreh Deah 308).

Ramban, may his memory be blessed, also wrote that when the father gives the money to the priest he should first give the child into the priest's hand, and the priest should say, "Which is more beloved to you, your son or these five sela?" And the father responds, "My son is more beloved to me." The priest immediately takes the silver coins and passes them over the head of the son and says, "This is in the place of this, traded for this, this is rendered no longer sacred through this. This goes out to the priest and this child should come to life and Torah and fear of heaven. May it be His will that as this one came to redemption, may he also come to Torah, marriage and good deeds, and let us say amen." The priest places his hands on the son's head and blesses him, according to how he knows to bless him, such as "May the Lord guard you, etc." (Psalms 121:5), or "As length of days and years of life, etc." (Proverbs 3:2) or "The Lord shall protect you from all evil and guard your soul, etc." (Psalms 121:7). And [the father] takes him out for all of his will. [This] and the rest of its details are elucidated in Tractate Bekhorot (see Tur, Yoreh Deah 308).