From old Christadelphian writings
Probably the reason why Paul circumcised Timothy was because he could not otherwise take him into the Temple (Num. i. 51). Timothy, too, was the son of a Jewess (Acts xvi. 1). It wasn’t, as some have suggested, simply to gain favour with the Jews, but to show that he was a good Jew, and that he had been slandered in being charged with having said that Jews ought not to circumcise their children (Acts xxi. 21).
“ And he came also to Derbe and to Lystra: and behold, a certain disciple was there, named Timothy, the son of a Jewess that believed; but his father was a Greek.” (Ac 16:1 ASV)
“ and they have been informed concerning thee, that thou teachest all the Jews who are among the Gentiles to forsake Moses, telling them not to circumcise their children neither to walk after the customs.” (Ac 21:21 ASV)
Paul never discountenanced circumcision as a national token; for he knew that it was such long before the Mosaic Law was given (Gen. xvii. 10; Acts vii. 8). Therefore, even when the Mosaic Law was abrogated, that, in itself, did not relieve the nation of the covenant token. But, be it remembered, Paul reprobated any suggestion that Gentile believers should be trammelled with any such rite or token (Gal. v. 2-12; vi. 12).
“ This is my covenant, which ye shall keep, between me and you and thy seed after thee: every male among you shall be circumcised.” (Ge 17:10 ASV)
“ And he gave him the covenant of circumcision: and so Abraham begat Isaac, and circumcised him the eighth day; and Isaac begat Jacob, and Jacob the twelve patriarchs.” (Ac 7:8 ASV)
“2 Behold, I Paul say unto you, that, if ye receive circumcision, Christ will profit you nothing. 3 Yea, I testify again to every man that receiveth circumcision, that he is a debtor to do the whole law. 4 Ye are severed from Christ, ye who would be justified by the law; ye are fallen away from grace. 5 For we through the Spirit by faith wait for the hope of righteousness.
6 For in Christ Jesus neither circumcision availeth anything, nor uncircumcision; but faith working through love.
7 Ye were running well; who hindered you that ye should not obey the truth? 8 This persuasion came not of him that calleth you. 9 A little leaven leaveneth the whole lump. 10 I have confidence to you-ward in the Lord, that ye will be none otherwise minded: but he that troubleth you shall bear his judgment, whosoever he be. 11 But I, brethren, if I still preach circumcision, why am I still persecuted? then hath the stumbling-block of the cross been done away. 12 I would that they that unsettle you would even go beyond circumcision.” (Ga 5:2-12 ASV)
“ As many as desire to make a fair show in the flesh, they compel you to be circumcised; only that they may not be persecuted for the cross of Christ.” (Ga 6:12 ASV)