The purpose of the British Columbia builders lien legislation (historically called the Mechanics Lien Act, now called the Builders Lien Act) has been described by courts as follows:
The end and object as well as the limitations of a mechanics' lien, a creation of statute, are, for the value of labour and materials, in the widest sense, applied to an improvement of land, to provide a security to those furnishing them in a legal charge upon the improvement and the land to which it has been added.
(Earl F. Wakefield Company v. Oil City Petroleums (Leduc) Ltd. et al.,  SCR 361).
[I]n Kettle Valley Contractors Ltd. v. Cariboo Paving Ltd. 1986 CanLII 1009 (B.C.C.A.) [McLachlin J.A., as she then was] cited at 251 Hickey v. Stalker, 53 O.L.R. 414,  1 D.L.R. 440 (C.A.) as correctly stating the purpose of mechanics lien legislation:
Speaking generally, the object of the Mechanics Lien Act is to prevent owners of the land getting the benefit of buildings erected and work done at their instance on their land without paying for them.
I would, as well, look at the matter from the perspective of those who supplied the materials or did the work on the land. The corollary of the principle expressed in Hickey (supra) is that the purpose of the Act is to protect those who contribute to the erection of buildings, or other physical improvements on another’s lands, and to ensure their payment by granting them a security interest in the land. The protection and the security in favour of a lien claimant come at the expense of the land owner, and of others having claims against the owner relating to the improvement which may be unsecured.
(Northern Thunderbird Air Ltd. v. Royal Oak & Kemess Mines Inc., 2002 BCCA 58 at para. 24 - 25).
More recently the British Columbia Court of Appeal has confirmed that it is a purpose of the Builders Lien Act to ensure that contractors and material suppliers are paid:
[An] important purpose of the statutory scheme is to ensure that contractors and workers are paid for materials provided and for services rendered.
(Bank of Montreal v. Peri Formwork Systems Inc., 2012 BCCA 4 at para. 60).